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Volume XXXI JULY, 1938 Number 1 



A Criticism of the Proposed Standards for 16-Mm. Sound-Film 


The Shrinkage of Acetate-Base Motion Picture Films 


Processing of Ultraviolet Recordings on Panchromatic Films 

J. O. BAKER 28 

An Optical System for the Reproduction of Sound from 35-Mm. 
Film J. H. McLEOD AND F. E. ALTMAN 36 

Push-Pull Recording with the Light- Valve 


Report of the Standards Committee 65 

The Influence of pR on Washing Films after Processing 


Problems Involved in Full-Color Reproduction of Growing 
Chick Embryo E. S. PHILLIPS 75 

Documentary Film Study a Supplementary Aid to Public 
Relations A. A. MERCEY 82 

New Motion Picture Apparatus 

An Ultraviolet Push-Pull Recording Optical System for News- 
reel Cameras G. L. DIMMICK AND L. T. SACHTLEBEN 87 

Overload Limiters for the Protection of Modulating Devices 


Current Literature 99 

Fall, 1938, Convention at Detroit, Mich.; Oct. 31st-Nov. 3rd, 
Incl 102 

Society Announcements 105 





Board of Editors 
J. I. CRABTREB, Chairman 



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Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

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Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1938, by the Society of 
Motion Picture Engineers, Inc. 

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'President: S. K. WOLF, RKO Building, Rockefeller Center, New York, N. Y. 
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'Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 
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J. O. AALBERG, 157 S. Martel St., Los Angeles, Calif. 
*M. C. BATSEL, Front and Market Sts., Camden, N. J. 
**R. E. FARNHAM, Nela Park, Cleveland, Ohio. 
*G. FRIEDL, JR., 90 Gold St., New York N. Y. 
*A. N. GOLDSMITH, 444 Madison Ave., New York N. Y. 
**H. GRIFFIN, 90 Gold St., New York, N. Y. 

**A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 
*S. A. LUKES, 6145 Glenwood Ave., Chicago, 111. 
*Term expires December 31, 1938. 
**Term expires December 31, 1939. 



Summary. It has been proposed that the standard dimensions of 16-mm. sound- 
prints be changed, principally by widening the sound record and scanned areas. The 
question is reviewed from the standpoint of the cumulative effects of film shrinkages 
and mechanical inaccuracies in the steps leading to the final sound-print and in the 
projection of that print, following the method described by R. P. May in the April, 
1932, Journal. 

A film having sound records of various widths supports the contention that in- 
creased width of sound-track is not needed, and that if any change from the present 
standard is to be made, it should be in the direction of a narrower track to provide a 
wider margin outside the sound-track and a wider safety area between the sound- 
track and the picture. 

The present dimensional standards of sound-film, both 35-mm. and 
16-mm., reflect the fact that sound was added to the motion picture 
long after these two film sizes had been standardized for silent pic- 
tures. The silent film standards necessarily limited the amount of 
space on the film that could be made available for the sound. How 
much more space the sound engineers would have liked to have can 
be seen by comparing our present standards with the wide films 
of 1929 and 1930, in which the sound-track was approximately three 
times as wide as the ones we use today. 

Because the space that could be taken for the sound record was 
thus limited, a second conflict of interests necessarily arose between 
two classes of sound engineers. What might be called the optico- 
photographic group naturally wished to use as much of the available 
space as possible for the sound-track. At the same time the mechani- 
cal engineer designing the sound equipment logically demanded a 
certain amount of space for mechanical handling of the film and for 
providing tolerances against inaccuracies in guiding. 

The compromise between the two requirements was bound to prove 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
May 4, 1938. 

** The Berndt-Maurer Corp., New York, N. Y. 



unstable in a rapidly advancing art. Every improvement in mechani- 
cal accuracy naturally encouraged those who wished to enlarge the 
sound-track at the expense of the safety areas. Conversely, every 
improvement in film stock or in recording or processing technic that 
increases the volume range attainable from the track might serve as 
an excuse for the mechanical designer to call for a relaxation of the 
narrow dimensional limits that hold him, as it were, in a strait- 
jacket. If he does not protest, it is because the mechanical engineer 
rarely lays claim to any very complete knowledge of photographic 
and optical requirements in recording and reproduction. Not feeling 
sure of his ground, it is only when he is pushed too far that he rebels 
against the tendency to increase the width of the track at the expense 
of the safety areas. 

In the JOURNAL of the Society for March, 1938, there appeared a 
report of the Standards Committee 1 in which a considerable number 
of revisions in the standards are proposed for adoption by the Society. 
So far as these revisions relate to sound, they consist mostly of in- 
creases in the width of the sound-track areas, with corresponding re- 
ductions in the width of what we have been calling the safety areas. 

The authors have studied with particular care the proposals relating 
to 16-mm. sound-films. Briefly, they feel that these new proposals 
seriously unbalance a situation that was already unfavorable for the 
mechanical designer, and that they do so without gaining any per- 
ceptible advantage in the way of better sound reproduction. There- 
fore, in response to the published invitation 2 to discuss the proposed 
revision of the standards, this analysis of the problem is presented by 
the authors as they see it. 

A brief historical review may serve to illuminate several of the 
points at issue. The present system of 16-mm. sound-film standards 
originated in the proposal made by R. P. May 3 at the Swampscott 
meeting of the Society in the Fall of 1931. The standard that Mr. 
May proposed was based upon a careful study of the various errors 
in track location that were likely to occur in going from a 35-mm. 
original sound-track through the steps of re-recording on 16-mm. film 
and contact-printing the resulting sound negative, followed by run- 
ning the print on a projector. A study was made also of the case in 
which the sound-track was directly re-recorded to the print. Adding 
up the possible errors, Mr. May arrived at the interesting conclusion 
that a film 0.660 inch wide (instead of the standard 0.630 inch) would 
be required to accommodate what he believed to be a sufficiently 


wide track, plus full provision for overlap of the scanning beam, and 
safety areas wide enough to provide for proper mechanical support. 
But, on the assumption that all the possible errors would hardly ever 
accumulate in one direction, it was believed possible to arrive at a 
workable standard within the limits of the 0.630-inch film. The 
standard that was proposed had substantially the same track width 
as the one that was adopted in 1934, but placed the track center-line 
0.045 inch from the edge of the film instead of at the present standard 
distance of 0.058 inch. A safety area 0.0284 inch wide was provided 
between the printed area of the sound and the printed area of the 

The standard that was set up in November, 1934, 4 is shown drawn 
accurately to scale in the top half of Fig. 1. It will be noticed that 
the safety area between the picture frame and the space allotted to 
variable-density sound-track was reduced to 0.012 inch. On the 
other side of the track was provided a fairly comfortable space of 
0.018 inch between the variable-density track and the edge of the film. 
But the principal objection to this standard was the small allowance 
for sound-track weave. The variable- width track was set at 0.060 
inch ; the scanned area was only 0.065 inch wide ; therefore, the al- 
lowance for weave was only 0.0025 inch in each direction, which is 
insufficient. So far as the authors are aware, no manufacturer of 
projection equipment followed the standard in this respect. Scanning- 
beam lengths used in practice varied from 0.070 inch to 0.080 inch 
with different manufacturers. 

After 1934, the process of optically reducing the sound-track from 
35-mm. negative to 16-mm. print became the most widely used 
method of producing 16-mm. sound-films. Certainly the excellence 
of the results that were attained justified the widespread adoption 
of the method. But this brought with it a complication of the stand- 
ards problem. Optical printers were designed to reduce the 0.071- 
inch variable-width track on the 35-mm. film to a width of 0.060 
inch on 16-mm. film. This ratio of 60 to 71 gave a reduced variable- 
density track having a width of 0.0845 inch instead of the 0.080-inch 
width called for by the 1934 standard. 

Eventually the 35-mm. standard was changed to specify a track 
space 0.076 inch wide in variable-width recording. This track, on 
the optical reduction printer, gave a 16-mm. print having a track 
width of 0.0642 inch. 

These two dimensions 0.0845 inch for the variable-density track, 








FIG. 1. SMPE standard. 

FIG. 2. One form of idler construction. 


and 0.0642 inch for the variable- width track are substantially those 
called for by the 1938 specification. As was logical, the width of the 
scanned area has been set at 0.074 inch, a value providing equal 
tolerances for weave on the two types of track. 

Thus, while the 1938 proposed standard follows present commercial 
practice, it seems to have been arrived at by a process of commercial 
evolution rather than by any process of careful analysis. Standards 
arrived at in this way are likely to contain defects that will sooner 
or later lead to a desire for modification. 

Before drawing definite conclusions, however, let us analyze the 
new standard step by step. In the first place, does it provide suitable 
allowance for side motion of the film and for accumulated inaccura- 
cies in the location of the sound-track? The method of study de- 
scribed by Mr. May should give the answer. 

The two processes in use today optical reduction and direct re- 
cording give about equal opportunities for mislocating the track. 
Let us study the optical reduction method. 

We have 35-mm. film carrying a sound-track that is officially per- 
mitted 5 to be 0.003 inch out of position, in the direction toward the 
picture. This film must be guided through one side of the optical 
printer. If the guiding is done by the best available means, it can be 
made accurate to about 0.001 inch, but hardly better than that. 
Thus, up to the point where the printing light-beam passes through 
the negative film, there is a possible error of 0.004 inch in the location 
of the 35-mm. track. Reduced through the optical system, this be- 
comes 0.0034 inch. 

The 16-mm. film must be guided also on the optical printer. Allow- 
ing again an error of 0.001 inch in guiding the film, the total possible 
error in track location on the 16-mm. film becomes 0.0044 inch. 

This film must be run on the 16-mm. projector. At the sound 
translation point it must again be guided. But at the sound transla- 
tion point the film needs to be left as free as possible to move with 
uniform speed, and this condition is not compatible with extreme ac- 
curacy of guiding. The method that most projector manufacturers 
have adopted is to pass the film between guide rollers or flanges placed 
a fixed distance apart. If the film is fresh, this method will guide it 
within 0.002 inch, but when shrinkage has reached a value of around 
one-half of one per cent,* the film is 0.003 inch narrower, and the 

* As set forth in a corollary paper "The Shrinkage of Acetate-Base Motion 
Picture Films," by J. A. Maurer and W. Bach (see page 15 of this issue), 


error in guiding is more likely to be 0.005 inch. Adding this to the 
error of location that may occur in printing, we find that the sound- 
track may in some cases be as much as 0.009 inch out of central 
location with respect to the scanning beam. 

The 1938 standard allows a tolerance of 0.005 inch before any part 
of the track misses the scanning beam. This is defensible on the basis 
that most of the time the errors enumerated above will partly cancel 
each other instead of adding, and therefore in most cases the total 
error will be less than 0.005 inch. 

Referring now to the picture standards, we find that the standard 
camera aperture is 0.030 inch wider than the standard projector 
aperture. This permits a weave of 0.015 inch toward either side of the 
picture gate, which is three times as much as is allowed for the sound- 

This difference becomes significant when we turn our attention to 
the matter of the safety areas. As shown in the lower half of Fig. 1, 
the safety area between the picture and the variable-density sound- 
track (or printed area) has now been reduced to 0.0095 inch. The 
safety area at the edge of the film has a width of 0.0155 inch. In these 
two narrow spaces the projector manufacturer must locate his sup- 
porting strips for handling the sound-track edge of the film where 
it passes around sprockets and rollers and where it is fed through 
the picture gate. 

Fig. 2 shows the type of idler construction that one prominent pro- 
jector manufacturer has been forced to adopt in the attempt to cope 
with this situation. If the observer remembers that the idler roller 
in this illustration is only J / 4 inch in diameter, he will realize how very 
tiny these two rounded ridges are. Yet they, and others like them on 
the sprocket drums and in the picture gate, are all the support it is 
possible to give to the sound-track edge of the film in its passage 
through the projector. 

It is the writers' opinion, based to a considerable extent upon ob- 
servation of what has happened to sound-prints in the field, that no 

the shrinkages to be found in current films in use measurably exceed the 0.5 
per cent assumed in this discussion. For example, it has been not unusual to 
find in film libraries film that has shrunk considerably more than 1 per cent. 
Recently it has been observed that there seems to have been a change in the base 
of this particular stock, which change indicates that 0.5 per cent will be a reason- 
able figure for the future. The stocks of other manufacturers point to the same 
possibility. The film manufacturers are to be commended for their progress in 
thus contributing to the solution of our knotty standards problem. 


type of metal, no method of plating, and no technic of polishing, 
can prevent the scratching of the film by a supporting strip as narrow 
as is required by this 1938 standard proposal. The pressure per unit 
area on the film is too great. Clean new films will go through a clean 
projector without perceptible scratching, but as soon as the film ac- 
cumulates a little dust and grit, the scratches appear. And, more 
often than not, they find their way into the scanned area, because 
weave in the picture gate and at the sprockets and idlers can not be 
reduced to zero. 

These remarks are not intended in any way as a criticism of the 
projector manufacturers or their products. The authors feel that the 
manufacturers have accomplished all that is mechanically possible 
within the limits imposed by the standard. But it is also felt that 
much better mechanical design would be possible if larger safety 
areas could be provided on the film. 

In order to provide larger safety areas we must either (a) reduce 
the width of the sound-track and scanned area or (b) reduce the al- 
lowance for picture weave. We suggest doing both, in moderation. 

The objectiqn will immediately be raised that any reduction of the 
width of the sound-track means a reduction of the available volume 
range. We propose to demonstrate that this loss is much less serious 
than it is commonly believed to be. 

Suppose that the modulated track-width of a record is reduced from 
0.064 to 0.060 inch. The difference in reproduction level is 0.54 deci- 
bel. A change of this magnitude is inaudible. If the track-width 
is reduced from 0.064 inch to 0.057 inch, the difference in reproduc- 
tion level is one decibel. This is about the smallest difference in level 
that can be detected. Volume controls on monitoring loud speakers 
and the like are commonly made with steps of two decibels. 

When the width of a sound-track is reduced, the background noise 
level diminishes almost, though not quite, as fast as the overall level, 
and the result is that the volume range is reduced much less than the 
volume level. Therefore, alterations in track-width that produce in- 
audible or barely audible changes in volume level, produce wholly 
negligible changes in volume range. 

(In order to permit the Society to judge these effects, the authors had prepared 
a number of recordings of a given musical selection, using different maximum 
track-widths. This film was played at the close of this presentation, to support 
the contention that no harm is done by moderately reducing the track-width.) 

To accomplish this reduction requires, of course, a modification of 


existing optical reduction printers. Such modification is not difficult. 
In many of the machines in use at the present time, a pair of cylin- 
drical lenses is used to obtain unequal magnification in forming the 
image longitudinally and laterally with respect to the sound-track. In 
most cases a slight change of the positions of these cylindrical lenses 
in the system is all that is required to give the necessary slight change 
in the lateral reduction ratio. 

Any change of standards must be made with caution in order to 
avoid impairing the performance of the large number of 16-mm. 
sound projectors now in use. In view of this consideration, we sug- 
gest that it is proper to retain the track- widths of the 1934 standard, 
which we know reproduce satisfactorily on existing projectors. 

These track-widths were 0.080 inch for the variable-density record, 
and 0.060 inch for the variable- width record. The present standards 
for 35-mm. film are 0.100 inch and 0.076 inch. If we adopt an optical 
reduction ratio of 0.8 instead of the present ratio of 0.85, we shall ob- 
tain track-widths of 0.080 and 0.0608 inch, respectively, for the vari- 
able-density and variable-width records. This is close enough to the 
1934 standards. The width of the scanned area can logically be made 
0.070 inch, which will give substantially the same tolerance for weave 
as the 1938 standard proposal. 

In case 35-mm. negatives having the old track-width of 0.071 inch 
are reduced on optical printers having an 0.8 ratio, a 16-mm. track- 
width of 0.0568 inch will be obtained. As has been pointed out, a 
track of this width is only one decibel lower in level of reproduction 
than the 0.064-inch track called for by the 1938 standard. Therefore, 
no perceptible sacrifice of performance is involved. 

The change of track-widths just discussed would gain 0.0025 inch 
for each of the two safety areas on the film. In order to gain addi- 
tional space for the safety area between the sound-track and the pic- 
ture, we suggest a slight change in the width of the standard camera 

This is by no means as revolutionary a suggestion as it may at first 
appear. A situation has existed ever since the introduction of optical 
reduction printing that has made it impracticable to conform exactly 
to the official standard. This situation came about because the ratio 
of height to width of the 35-mm. projector aperture as standardized 
after the introduction of sound is not quite the same as the ratio of 
height to width of the standard 16-mm. projector aperture. It is 
not easy to decide whether to reduce the picture in the ratio of the 


heights or in the ratio of the widths. It has been suggested by the 
Standards Committee that the Society ought to establish a standard 
reduction ratio for printing picture on 16-mm. film from 35-mm. nega- 
tives, but no final decision has been taken. 

This ratio problem has been subjected to thorough analysis by G. 
Friedl, Jr., 6 with whose conclusions we are in general agreement. 
Mr. Friedl recommends that the ratio of reduction be established as the 
ratio of the widths of the 35-mm. and 16-mm. projector apertures, that 
is to say, the ratio 0.825 to 0.380. If this is done the reduced image 
of the 35-mm. camera aperture is 0.400 inch wide. We suggest that 
this be made the standard width of the 16-mm. camera aperture, the 
projector aperture standard remaining unchanged. This will give 
a standard to which 16-mm. optical reduction prints can conform. 

In one particular we wish to suggest a deviation from the recom- 
mendations of Mr. Friedl. In the 35-mm. standards there is a displace- 
ment of 0.006 inch between the center-line of the camera aperture and 
the center-line of the projector aperture. This is provided as an 
allowance for shrinkage. Mr. Friedl has recommended that the 
optical reduction printer be adjusted so as to place the center-line of 
the image of the area covered by the 35-mm. projector aperture on 
the common center-line of the 16-mm. camera and projector aper- 
tures. This gives an image of the 35-mm. camera aperture that is off 
center a trifle less than 0.003 inch, in the direction of the sound-track 
edge of the film. As Mr. Friedl has mentioned in his paper, this dis- 
placement is in the wrong direction to serve as a shrinkage allowance, 
since the 16-mm. standard assumes that the film is to be guided by 
the sound-track edge. 

The authors suggest that the center-line of the image of the 35-mm. 
camera aperture, not the projector aperture, be made to coincide 
with the center-line of the 16-mm. film, which is the same as the 
center-line of the 16-mm. camera and projector apertures. This will 
give a margin of 0.010 inch of picture on each side of the 16-mm. pro- 
jector aperture. The shrinkage that occurs during the first few pro- 
jections of the print will then move the center-line in the proper 
direction to make the 16-mm. projected area identical with that pro- 
jected from the 35-mm. film. 

No harm will be done by changing the 16-mm. camera aperture 
standard to a width of 0.400 inch, since an allowance of 0.010 inch 
for picture weave will remain. This is sufficient for the modern pro- 
jector, as is proved by the successful projection of optical reduction 



prints in the past. At the same time a space of 0.005 inch will have 
been added to the safety area between picture and sound. 

A suggested set of specifications embodying these two changes is 
shown in an enlarged true-to-scale drawing in Fig. 3. It will be noted 
that the safety area between the picture and the sound-track is now 
0.017 inch wide instead of 0.0095 inch; that the two safety areas are 
of nearly equal width, the one of the edge of the film being 0.018 inch 


Proposed specifications. 

wide; and that the allowances for weave of picture and sound have 
been brought more nearly into agreement. 

We believe that this set of specifications, if put into use, would 
cause substantially no difficulty during the period of transition, since 
films made in accordance with it would reproduce satisfactorily on 
existing projectors, while projectors built in accordance with this set 
of specifications would give satisfactory results with film made on 
existing optical reduction equipment. At the same time the changes 
are not trivial, since they result in nearly doubling the space available 
to the projector manufacturer for the placement of his film supports, 


and thus make possible longer life and better performance on the part 
of both projector and film. 

The philosophy that is the basis of this entire discussion can be 
stated very briefly. We believe that better and more uniform sound 
can be reproduced from an undamaged track of moderate width than 
from a wide track that has been mutilated by scratching. Further, 
we believe that improved overall performance can be achieved under a 
set of specifications that provides for the customary machine-shop 
tolerances in making the parts that touch or support the film in the 

We recognize that certain assumptions have been made through- 
out this discussion that may not be in agreement with the opinions of 
others. Further discussion seems desirable. We suggest, therefore, 
that action upon the proposed standards for 16-mm. sound-film be 
postponed until a more complete consensus can be obtained. 


1 "Revision of SMPE Standards Proposed for Adoption by the Society," J. 
Soc. Mot. Pict. Eng., XXX (Mar., 1938), No. 3, p. 249. 
8 Ibid, p. 249. 

3 MAY, R. P.: "Sixteen-Mm. Sound-Film Dimensions," /. Soc. Mot. Pict. Eng., 
XVIH (Apr., 1932), No. 4, p. 488. 

4 "Standards Adopted by the Society of Motion Picture Engineers," J. Soc. 
Mot. Pict. Ewg., XXIII (Nov., 1934), No. 5, p. 247. 

6 C/ref. 1, p. 267. 

6 FRIEDL, G., JR.: "Data Regarding Dimensions of the Picture Image in 
16-Mm. Reduction Printing," /. Soc. Mot. Pict. Eng., XXVIII (June, 1937), No. 
6, p. 585. 


MR. CARVER: I should like to compliment Mr. Maurer for what seems to me 
to be the best criticism of a standard that I have ever heard at one of these meet- 
ings. It is to get such opinions as this that we publish the drawings as proposals, 
before validation by the Board of Governors. During the Committee's dis- 
cussions of the drawings the dimensions were changed several times, mainly to 
keep up with changes that the manufacturers were making during the time. 
None of them seemed very satisfactory and we felt that it would be best to pub- 
lish the drawings for wider criticism. The two drawings DS35-7-1 and DS 
16s-7-l, showing the 35-mm. and 16-mm. sound-tracks, were not validated as 
SMPE standards at the Board meeting on April 24th, and as a consequence are 
up for further study and alteration, if advisable. We hope, with the aid of your 
analysis, to arrive at a satisfactory answer. 

MR. OFFENHAUSER: Mr. Maurer and I were not associated with the Stand- 
ards Committee, and became aware of the nature of the Committee's deliberations 


only when we received our copies of the JOURNAL for March, of this year, in which 
the proposed standards were printed. 

While we have been interested in standards for a number of years, it was only 
about six months ago, and for entirely different reasons, that we began making 
shrinkage and other measurements, the results of which are applicable to this 
problem. Our direct preparation for this paper began when the proposed stand- 
ards were published, and only at that time did we begin to collect data related 
specifically to the problem. It takes time to collect data. I believe that this 
procedure has to be followed in practically every instance where comment is 
made from outside the Society's Committees, in order that those offering the 
comment may be sure of their ground. We felt that a communication at this 
time was proper, inasmuch as the Standards Committee published an invitation 
to discussion in connection with the new standards proposal. 

MR. TOWNSLEY: I hope that the Standards Committee will give some thought 
to arranging the final dimensions so that the lateral reduction ratio for optical 
reduction printing will be the same for variable-density and variable-width 

MR. KELLOGG: We want to make sure that any step we take will be toward 
higher standards of performance, even if it should make certain jobs a little more 
difficult today, provided we do not make them excessively expensive. 

Sometimes changing a standard in one direction may be a very simple matter 
while changing it in the other direction may mean serious difficulty. Regardless 
of the dimensions of the sound-track as now proposed, I do not see why the length 
of the scanning-beam in a projector should not be about as long as one can make 
it without getting over into the edge that needs the support, and coming danger- 
ously close to the picture frame line. If many projectors are built with shorter 
scanning-beams, it will be practically out of the question to adopt a wider track 




Summary. A simple direct-reading film-shrinkage gauge has been constructed 
with which shrinkage readings may be made in a few seconds. The accuracy of the 
instrument is such that the maximum variation in a series of readings made upon a 
particular film will not be more than 0.02 per cent of the predetermined length mea- 
sured. Readings have been taken systematically with this instrument over a period 
of five months to determine the shrinkage behavior of acetate-base films under various 
conditions of storage and use. 

The results indicate that the safety-base film made by each of the three American 
manufacturers has a characteristic value of shrinkage that is ordinarily reached within 
a few days after processing. Subsequent shrinkage is slow but continuous over a long 
period of time. The ultimate shrinkage is of the order of 1.25 per cent except in the 
case of films that have been projected many times on projectors using high-wattage 
lamps. The bearing of this shrinkage information upon equipment design is dis- 
cussed briefly. 

Ever since motion picture films were first made, it has been recog- 
nized that they shrink as a result of exposure to the air and to the 
various chemical baths used in the film laboratory. It has also been 
recognized for a long time that the shrinkage of acetate-base, or safety, 
films is greater than that of nitrate-base films, and, in fact, this is 
one of the principal reasons for the continued use by the industry of 
inflammable films in preference to safety films. The literature of the 
art contains numerous references to the fact of shrinkage but very 
little quantitative information about it. This is unfortunate, inas- 
much as it is hardly possible to arrive at a comprehensive design of any 
part of a motion picture machine having to do with the handling of 
film without at least making some assumptions as to the range of film 
dimensions within which the machine will be required to operate. 

With regard to nitrate-base film it is possible to gain at least a fair 
idea of these limits by studying the published material on sprocket 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 15, 1938. 

** Berndt-Maurer Corp., New York, N. Y. 


16 J. A. MAURER AND W. BACH [J. S. M. P. E. 

design. With respect to acetate base, however, a careful search of 
the past publications of the Society has indicated that they contain 
no information of any appreciable value about the shrinkage of this 
basic raw material of the-16-mm. industry. 

As a first step toward the accumulation of a body of facts as to the 
shrinkage of safety-base films, the authors constructed the shrinkage 
gauge shown in Fig. 1. This gauge operates upon the simple principle 
of magnifying by a lever the differences in length occurring over 39 
sprocket-holes of the 16-mm. film. One sprocket-hole is placed over 
a fixed pin at the left side of the gauge. The 39th sprocket-hole to the 

FIG. 1. The shrinkage gauge in use. 

right of this is placed over a pin on the short end of the lever. Be- 
tween these two points the film lies in a channel between two parallel 
plates of metal separated by twice the thickness of the film. The up- 
per of these plates is a flap which is closed down after the film has 
been laid in place. This arrangement serves to assure that the film 
will lie straight without kinks between the two measuring points. A 
light coiled spring attached to the pointer applies enough tension to 
overcome any tendency of the fulcrum bearing to stick, and to take 
up any possible looseness in this bearing, but does not apply enough 
pressure to cause the pin on the end of the lever to distort the edge 
of the sprocket-hole at which the reading is being taken. 

The distance corresponding to 39 sprocket-holes was chosen as the 

July, 1938] 



length of film to be measured because this length leaves no uncer- 
tainty as to which sprocket-hole is the one to be placed over the pin 
on the end of the lever, and thus it is not necessary for the person us- 
ing the gauge to count the number of sprocket-holes in the length he 
is measuring. Thirty-nine holes were chosen, instead of the round 
number of 40, because this permits calibrating the gauge by the aid of 
an ordinary 12-inch machinist's vernier caliper. The scale was cali- 
brated so that each division corresponds to 0.1 per cent of the stand- 
ard perforation length for 39 sprocket-holes, plus the height of one 
sprocket-hole, which must be added because the two pins on the gauge 
are in contact with opposite sides of the sprocket-holes in which they 
are placed. This is 11.750 inches. Without introducing doubt as to 
which sprocket-hole was the cor- 
rect one on which to measure, it 
was found possible to make the 
scale read all lengths from 1.0 
per cent longer than standard 
pitch to 2.0 per cent shorter 
than standard pitch, as shown 
in Fig. 2. Since we were think- 
ing of shrinkage as a positive 

FIG. 2. The scale on which shrinkage 
readings are indicated. 

quantity, the points on the scale 

corresponding to lengths of film 

greater than the standard were 

marked as "negative" shrinkages, 

and points corresponding to lengths of film less than the standard 

were marked as "positive." Thus, when the pointer stands at, for 

example, the line marked .5, this signifies that the film being measured 

is one-half of one per cent shorter than the standard pitch. 

The pointer of this instrument is relatively long and fragile, and it 
was considered possible that it might be bent by accident, which would 
result in false readings. To provide an easy means of checking the 
accuracy of the gauge we constructed the master test-bar shown in the 
upper left-hand part of Fig. 1 and in use on the shrinkage gauge in 
Fig. 3. The space between the stops at the ends of this bar was made 
11.750 inches plus or minus 0.001 inch. By placing this test-bar upon 
the gauge, as shown in Fig. 3, and noting whether or not the pointer 
reads exactly zero, one can check the accuracy of the instrument in a 
very few seconds. 

With this gauge on a rewind table a series of readings giving the 

18 J. A. MAURER AND W. BACH [j. S. M. P. E. 

state of shrinkage throughout a reel of film can be made in a few 
minutes. The time required to take an individual reading is no longer 
than the time required to write out the result in a notebook. The 
readings are reproducible to about two-tenths of the distance between 
adjacent divisions on the scale, or within about 0.02 per cent, without 
exercising any unusual care in handling the gauge. 

We began using this gauge in October, 1937, taking readings on such 
pieces of film as passed through our hands in the course of regular 
work, and noting the results in a small book which was kept with the 
shrinkage gauge. In the course of a few days we noticed so many in- 

FIG. 3. Checking the gauge by means of the test-bar. 

teresting facts that we were impelled to begin making a systematic 
series of readings on two pieces of film that happened to have been 
processed under identical conditions on the same day. For. con- 
venience we shall refer to the manufacturers of these two pieces of 
film as manufacturer No. 1 and manufacturer No. 2. 

The two films were kept on separate reels and were stored in an 
ordinary filing cabinet in two identical 400-foot cans of the type used 
for packing film for use in laboratories. Both the films were of the 
"positive" type used for making sound and picture prints. The cans 
were kept closed when the film was not being handled, but were not 
sealed with tape. The lids fitted closely, but not closely enough to 
exclude air and moisture. In short, conditions of storage corresponded 
roughly with the conditions under which sound or picture nega 

July, 1938] 



lives are commonly stored. The air of the building was not condi- 
tioned, and therefore the humidity varied according to the general 
state of the weather. Each day for a period of a little more than five 
months, except on Sundays and holidays, each of these films was re- 
wound, and during the rewinding the shrinkage was measured at six 
points throughout its length, these points being identified by punch 
marks in the film outside the length being measured. 

The behavior of the two films during this five months' period is 
shown in Fig. 4. Each point plotted on these curves is the average 
of the six readings taken on the particular day in question, these six 
readings invariably agreeing within 0.05 per cent. Therefore we are 




> r 



















v OS 






r 05- 
















/" * 




0) w - 




" 03 







FIG. 4. Shrinkage of two samples of acetate-base film measured daily over a 
five-month period. 

confident in stating that the apparently erratic variations in length 
indicated on these graphs are real variations and not the result of 
inaccuracy in the shrinkage gauge. Each vertical line on the graph 
represents a period of one week ; the months are shown at the bottom 
of the figure. 

It will be noted that the two films on the day they were processed 
both showed a shrinkage of 0.2 per cent. Two days later when the 
next reading was taken, these shrinkages had increased to 0.4 per 
cent for the film of manufacturer No. 1, shown in the upper curve, 
and 0.29 per cent for the film of manufacturer No. 2, shown in the 
lower curve. Two days later still, the values were 0.45 and 0.31 per 
cent, respectively. These values are generally representative of 



[J. S. M. P. E. 

what we have observed in other samples of film of the same manu- 
facturers. It will be noted that the shrinkage that occurred during the 
first two days after processing was as great as the further shrinkage 
that occurred during the next two weeks. It will be noted also that, 
disregarding erratic variations, which we will endeavor to explain 
later, the shrinkage after the first two days occurred at a practically 
uniform rate over the following six weeks. After that, the rate of 
shrinking decreased gradually until after three months the curves 
seem to indicate that a condition of stability has been reached. 

It will be noted that the apparently erratic variations above and 
below the general trend of the curves show a definite correspondence 




FIG. 5. Enlargement of a section of Fig. 4 to show cor- 
relation between shrinkage and weather conditions. 

in the two curves. This is especially easy to see during the two weeks 
following the start of the series of measurements and over the part of 
the curve after a condition of approximate stability has been reached . 
We noticed as the series of measurements proceeded that these varia- 
tions above and below the general trend could be correlated with the 
changes in weather conditions, and therefore with the general hu- 
midity of the air. Fig. 5 has been plotted to show this correlation more 
clearly. In this figure the character of the circle drawn around each 
point observed shows the weather prevailing at the time the measure- 
ment was made. An open circle indicates fair weather with the sun 
shining. A circle containing a cross indicates cloudy weather. A 
circle completely filled in indicates rain. It can be seen from Fig. 5 
that the film, even though kept in a closed metal can and exposed 
directly to the air for only a few minutes each day, is able to absorb 

July, 1938] 



enough moisture during periods of high humidity to expand by as 
much, in some instances, as 0.04 per cent, and that on the other hand 
it loses this moisture during periods of lower humidity within as 
short a period as two days during which it is not handled at all. Ap- 
preciable absorption or loss of moisture does not occur during the time 
required to take the readings, as is proved by the fact that the read- 
ings on any given day are consistent from one end of the film to the 

While the film is able to take up and lose moisture in this way if 
it is kept in an unsealed can, we have found that a strip of ordinary 





- , 

-^" - 







X ' 



- A_ 


> o < 
j k j 





^_ ^> 



>P ^.^j 




. " 


? NO.I 


NO. 2 





FIG. 6. 



Shrinkage of three samples of fresh raw stock freely exposed to air. 

adhesive tape around the joint of the can seals it very effectively. A 
roll of processed film placed in the ordinary 400-foot can and sealed 
in this way will shrink less than 0.1 per cent over several weeks. The 
same conclusion may be drawn from the behavior of raw stock, which, 
as we shall show, shrinks very rapidly when freely exposed to the air, 
but shows not more than 0.15 per cent change in length even when 
kept in storage for several months. 

Fig. 6 shows what happens when strips of raw stock freshly taken 
from the original package are hung up so as to be exposed to the air 
on both sides. The vertical lines in this figure represent half -hour in- 
tervals, the entire experiment extending over eight hours. The films 
of manufacturer No. 1 and manufacturer No. 2 were from fresh 
stock, and showed a shrinkage value of the order of 0.05 per cent 



[J. S. M. P. E. 

when first taken from their cans. The strips were not taken from the 
very outside of the roll but from a point about one-quarter of an inch 
in. The sample from manufacturer No. 3 had been in stock for about 
two months, and therefore it is perhaps not fair to compare it with the 
other two samples, though the results are in accord with our other 
observations in connection with the stock of manufacturer No. 3. It 
will be noted that each of the samples underwent a shrinkage of the 



MAN ffiMTi Wll MO. 3 

FIG. 7. Shrinl^age of three samples of film as affected 
by use on a projector. 

general order of 0.2 per cent within the first hour and a half, and that 
thereafter the shrinkage is much slower. The day on which this ex- 
periment was made was rather humid, and for that reason the total 
shrinkage in the curves of the 8-hour period is not as great as we 
should ordinarily expect on the basis of other observations. 

Thus far our experiments were directed principally toward deter- 
mining what may be expected to happen to negative films under the 
conditions of storage and use for printing in film laboratories. When 
we decided to present this material in the form of a paper before the 
Society it seemed desirable to acquire some information about the 


behavior of prints as used on projectors. For that purpose we made 
up a reel consisting of three prints of the same subject on the three 
types of raw stock, all the prints being processed at the same time. 
Immediately after processing we measured the shrinkages at several 
points in each section of the film, and thereafter for a period of two 
weeks we projected the film twice daily on a projector having a 
1000- watt lamp operated at 95 per cent of its rated voltage. The 
series of measurements was repeated before and after each running 
of the film on the projector. The results are shown in Fig. 7, in which 
the broken lines pass through the points measured before running 
the film through the projector and the solid lines pass through the 
points measured after projection. It may be noted that the film 
shrinks unmistakably during each projection and in most cases does 
not reabsorb enough moisture to regain its earlier length before the 
next time it is projected. However, these curves do display in a 
striking fashion the effect of three successive days of heavy fog and 
drizzling rain, which occurred late in March. The moisture in this 
case was absorbed by the film in some instances so rapidly as to can- 
cel the ordinary drying effect of the heat of the projector lamp. 

In the test shown in Fig. 7 the films of manufacturer No. 2 and 
manufacturer No. 3 behaved as would have been expected from our 
previous observations, but the film of manufacturer No. 1 shows a 
radical departure from its previously observed performance. On the 
basis of all previous observations we should have expected the curve 
for manufacturer No. 1 to lie between the curves for manufacturer 
No. 2 and manufacturer No 3, but on the contrary we find that the 
film of manufacturer No. 1 here shows a much lower value of shrink- 
age, and even after repeated passages through the projector has 
reached a shrinkage of only 0.3 per cent, a value comparable to the 
shrinkages observed in nitrate-base films and one that would ordinar- 
ily be reached within a few hours after processing. We do not know 
whether to attribute this to some factor that escaped our attention 
in the handling of the three films or to a change in the nature of the 
film-base itself, but we have not at any other time observed a sample 
that showed as low a shrinkage value as this particular sample. If 
the change in behavior is due to a change in the nature of the stock, 
it is to be hoped that this manufacturer will continue to supply stock 
having these characteristics. 

In addition to these more or less systematic studies of the be- 
havior of films under specified conditions, we have made many ran- 

24 J. A. MAURER AND W. BACH [j. s. M. p. E. 

dom measurements of films processed at various times and handled 
under various conditions. These measurements serve only to call 
attention to the great complexity of the problem presented by film 
shrinkage. We have been unable to arrive at any general conclusions 
as to the effect of processing conditions, since films processed in differ- 
ent laboratories some by the rack-and-tank method and some by 
automatic machine all measure about the same length after they 
have been in storage for several months. Films that have been 
stored in unsealed tin cans show no markedly less shrinkage than films 
stored in cardboard containers. At one tune we felt that we were 
justified in assigning a characteristic value of shrinkage of 0.5 per cent 
to the film of manufacturer No. 2, 0.7 per cent to the film of manu- 
facturer No. 1, and 0.9 per cent to the film of manufacturer No. 3 
under the conditions of our observations. Recent behavior of these 
film stocks, however, does not justify our making these generaliza- 

The value of ultimate shrinkage is of considerable importance, since 
it affects the design of sprockets wherever used. The bearing surface 
diameter of a hold-back sprocket is directly determined by the maxi- 
mum shrinkage to be accommodated, and the thickness necessary 
at the base of the tooth of any sprocket is determined by the maximum 
shrinkage, the minimum shrinkage, and the number of teeth in mesh. 
In our stock of old films, some of which are as old as six years, we 
have found only one film that was shrunk more than 1.25 per cent. 
That was on the stock of manufacturer No. 1 and showed a shrink- 
age of 1.4 per cent. It was about five years old. On the other hand, 
films belonging to film libraries on which we have been able to take 
measurements sometimes showed shrinkages as high as 1.6 per cent. 

It is possible that all our measurements are profoundly influenced 
by the fact that they were made in New York City, where the average 
humidity is considerably greater than it is in other parts of the United 
States. In view of the direct evidence that we have presented, that 
moisture absorption can cause an actual lengthening of the stock, we 
feel that our results as to the ultimate degree of shrinkage are of little 
value except as applying strictly to New York City conditions. 

It is clear that we have only scratched the surface of a very large 
and complicated problem. The most casual reflection will suggest a 
large number of experiments that might be tried to determine the 
influence of such factors as humidity, surface treatment of the film (as 
by anti-scratch processes), temperature of storage, etc. 


One fact we feel has been definitely revealed by these studies. 
Acetate film base is not a definite product having definite physical 
constants; its properties can be made to vary over a wide range by 
different methods of manufacture. We feel that with further ex- 
perimentation on the part of the manufacturers there is a possibility 
that safety films may be produced, at least for record purposes and 
in general for all applications where permanence is desired, having 
shrinkage properties comparable to those of nitrate-base film. 

We have made no comparisons of different film stocks on the basis 
of strength, flexibility, or any physical properties other than shrink- 
age. Such comparisons as we have made between the stocks of 
different manufacturers relate only to the one point of shrinkage be- 
havior. We hope that the results that have been presented here will 
prove sufficiently interesting to stimulate others to undertake similar 
studies and to publish their results. 


MR. BRADLEY: The subject of this paper is of great interest to the National 
Archives and the National Bureau of Standards. There is a project at the Bureau 
of Standards that has been going on for about three years under the general title 
of "Reproduction of Records," but actually it has turned out to be a considera- 
tion of preservation of records, and one of the items considered was the shrinkage 
of film. 

Mr. Maurer's device for measuring the shrinkage is a distinct contribution. 
The results of our own studies, in which shrinkage was observed under controlled 
predetermined humidity, were published in the December, 1937, Journal of Re- 
search of the National Bureau of Standards. We found that the film shrinks 
very rapidly in the first ten days in ovens where the humidity is under control. 
We are now trying to determine the percentage of shrinkage in aerial-mapping 
film, where the accuracy must be very great to prevent ground distortion. A 
very small shrinkage of an aerial map may produce distortion equivalent to as 
much as sixteen feet on the ground, depending upon the elevation of the camera 
at the time the exposure was made. 

Mr. Maurer stated that on three rainy days the moisture content of the film 
rose very rapidly. Did the studies include measurement of the restoration of 
moisture to the film? 

MR. MAURER: No, they did not. We only infer that moisture was taken up 
because of the very definite correlation between shrinkage and state of the 

MR. BRADLEY: Would it be an advantage to measure it? 

MR. MAURER: I believe that it would. However, we do not have facilities 
for making such measurements. 

MR. BRADLEY: We have developed a technic for restoring the moisture con- 
tent in film. It consists in rewinding the film slowly, through what we call a re- 
humidifier, and blowing moisture across the surface of the film. If the film is 

26 J. A. MAURER AND W. BACH [J. s. M. p. E. 

closely wound in rolls, as many as six months may be required for the moisture to 
penetrate to the interior of the roll. 

MR. KELLOGG: I do not suppose that you have made measurements of film 
from which the gelatin has been removed. The question does not enter, so far as 
I can see, into the practical problem that you are investigating, but it might be 
of interest to be able to separate the effect of moisture upon the gelatin from the 
effect upon the base. There are some problems in connection with which we are 
interested in the action of moisture on the base alone. 

MR. MAURER: No measurements of that sort have been made. However, 
in the piece of film that was projected at regular intervals we provided areas that 
were transparent and other areas were exposed to complete opacity so far as was 
possible, and care was taken in making the measurements to include both the 
transparent and the completely opaque areas. We found no consistent difference 
between the shrinkage behaviors of these two sections of the film. We expected 
to find such a difference, because the black film would presumably absorb heat 
during projection more completely than the transparent film, but to our surprise 
we found no difference. 

MR. FRIEDL: Several years ago some shrinkage measurements were made in 
an exchange in New York on 35-mm. film, checking the films as they went out and 
as they were returned after being shown in several theaters, plotting the shrinkage 
against age and use, and keeping records of the weather during that period. 
Our observations, I should say, were very similar to Mr. Maurer's with respect to 
the stretching of the film on wet days. 

MR. GRIFFIN: I noticed that your shrinkage measurements were longitudinal 
shrinkages. In such measurements as I have made, on 35-mm. nitrate-base 
stock, I have found that the lateral shrinkage is far greater than the longitudinal. 
I am wondering whether that is so in the case of acetate-base stock, and whether 
you used the longitudinal shrinkage figures in computing the figures you gave for 
the placement of the sound-track. 

MR. MAURER: The answer is yes. We used the longitudinal shrinkage 
figures. We have not made direct measurements of the lateral shrinkage of 16- 
mm. film. A number of years ago I had occasion to do a piece of work that ex- 
tended over about a year, that showed at that time very accurate agreement be- 
tween longitudinal and lateral shrinkage of, as it happened, acetate-base films. 
However, those films were not subjected to the conditions encountered when a 
film is projected, and therefore the result arrived at then, that the longitudinal 
and lateral shrinkages were the same, is not valid as applying to the conditions 
of actual use of 16-mm. films. Mr. Griffin has raised a very important question 
and one on which we shall endeavor to throw some light if we can devise a satis- 
factory method of making the measurements. 

MR. MITCHELL: Has anybody investigated what might be described as the 
"warping" of 16-mm. sound-film, caused by the film having sprocket-holes on 
one side and not on the other? It is found more particularly in 8-mm. film, but 
also in 16-mm., that the shrinkage is not the same along the two sides. Greater 
shoe service between the picture and the sound area takes care of any very slight 
wrinkling that may occur that would affect the sound quality, and would help to 
keep the film down and within the depth of focus of the scanning lens. 

MR. DEPUE: I had occasion to try to make some reduction prints from a 60- 


mm. film that I had in 1897, and I had a sprocket-wheel that fitted the film at 
that time. When I came to make the reduction I looked up the old sprocket- 
wheel and found that the shrinkage sidewise at the perforations was more than 
VM inch, not by accurate measurement, but rough observation. Longitudinally 
the sprockets seemed to fit all right over the four or five teeth the film engaged. 
The film was a nitrate negative film, kept in ordinary storage. 

MR. IVES: V. B. Sease in a paper published in the Transactions of the Society 
("Moisture in Motion Picture Film," 12, No. 34, p. 390, April, 1928) showed 
some interesting effects of fluctuating moisture content upon the dimensions of 
cellulosic films. More recently, Weber and Hill ("The Care of Slide-Films and 
Motion Picture Films in Libraries," J. Soc. Mot. Pict. Eng., XXVII, Dec., 1936, 
p. 691) studied the interrelations of shrinkage, moisture content of film, and 
humidity of surrounding atmosphere for the safety type of film. In another 
paper published about the same time by the same authors ("Stability of Motion 
Picture Films as Determined by Accelerated Aging," /. Soc. Mot. Pict. Eng., 
XXVII, Dec., 1936, p. 677) safety-film was reported to be stable and lasting in 
accelerated aging tests. While their judgments were based upon tests of chemical 
and mechanical properties, their conclusions are of interest in connection with the 
topics under discussion. Davis and Stovall ("Dimensional Changes in Aerial 
Photographic Films and Papers," Research Paper 1051, J. of Research Nat. Bur. 
of Standards, 19, Dec., 1937, p. 613) have commented favorably upon the shrink- 
age characteristics of some samples of acetate film tested in comparison with 
films of the type used for aerial mapping. 


J. O. BAKER** 

Summary. The necessity in newsreel work of making the original sound re- 
cording on panchromatic film has always meant a serious sacrifice in quality and 
ground-noise ratio, as compared with results that can be attained when sound is 
recorded on a separate film. While ultraviolet recording materially increases fidelity 
of response, with panchromatic as well as with standard sound negative film, the 
low contrast and high base fog of panchromatic film processed for negative picture 
development produce noise and considerable reduction in volume range. 

The track density on the panchromatic film is rather low, of the order of 1.0 to 1.2, 
when recorded with a practical optical system for a single- film system. When this 
track is printed on commercial release print stock the dense portion of the negative 
track will print through, producing a fog density in the clear portion of the printed 
track. This fog in the clear portion tends to produce noise and reduces the volume 
range. When the panchromatic negative and print are processed in accordance 
with commercial practice, the reduction in volume range is of the order of 6 db. 

Printing panchromatic negative upon a high-contrast emulsion improves both 
the noise and volume range. Since the release prints must be on standard picture 
positive stock and not on high-contrast film, it is proposed to make a master positive 
on high-contrast emulsion and to re-record from this to a standard sound negative, 
which would be used in the ordinary way to make the release prints. An improve- 
ment in release print ground-noise of 8 to 12 db. is obtained by this method, and the 
volume range is increased by 6 db. Briefly, the proposed method is a means for 
increasing the density contrast of the final release print track when the original is 
recorded on panchromatic film. 

It has long been known that emulsions with fine grain and high 
contrast gave superior results for variable-width sound recording. 
The investigations made by Hoxie of the General Electric Company 
in 1921 led to the adoption of positive types of emulsion for this pur- 
pose; however, in single-film systems, where the picture and sound 
are recorded simultaneously on the same film, the sound must be 
subordinated to the picture. The coarse grain of panchromatic 
emulsion together with the method of picture processing for an over- 

* Presented at the Spring, 1938, Meeting at Washington, B.C.; received 
April 15, 1938. 

** RCA Manufacturing Co., Camden, N. J. 



all gamma of unity produces sound-tracks of poorer quality than 
can be obtained with fine-grain recording emulsions. 

This paper describes the results that can be obtained when vari- 
able-width sound-tracks are recorded with ultraviolet light on pan- 
chromatic film and printed with ultraviolet light on motion picture 
positive film and processed in accordance with the commercial tech- 
nic for motion pictures, as well as the employment of a high-contrast 
emulsion for use as a master positive. Image definition of panchro- 
matic emulsion is somewhat poorer than that of positive emulsions. 

FIG. 1. Sensitometric characteristics for sound 
recording: Panchromatic in D76, 8Vz min., 60F; 
motion picture positive in D16, 4 J /2 min., 65F; high- 
contrast positive in "Dev. A," 13 Va min., 65 F. 

.e ultraviolet filter is used in the recording to reduce the image 
spread and to improve the response at the higher frequencies. This 
permits recording at a higher track density, but limits the maximum 
density attainable due to the restriction of the recorder light to a 
narrow spectral band. 

With white-light recording on panchromatic film, the best results 
were attained with equal negative and print densities, of approxi- 
mately 0.80. These were the conditions that most nearly fitted the 
requirements for minimum image distortion in motion picture posi- 



[J. S. M. P. E. 

tives. Ultraviolet recording reduces the image spread in the nega- 
tive thereby permitting a higher density in the recorder track. 

The base or fog density of panchromatic film is approximately 
0.34, and with a recorded track density of 1 or greater, the difference 
in transmission through the dense and clear portions of the track is 
considerably reduced. The printer light will, therefore, penetrate 
the clear portion and produce an exposure on the print which for a 

1000~High-Contraat Print 

Made from UV Panchromatic Nagatlva 
Track Density 1.0 
Fog Dentlty 0.34 

FIG. 2 (A). Panchromatic sound recording: cross- 
modulation characteristics. 

perfect track should be unexposed. This exposure or fogging of the 
clear portion of the positive track results in reduced output as well 
as increased noise. 

By the use of a high-contrast emulsion for printing a master posi- 
tive for use in re-recording, the fog density in the clear portion will be 
materially reduced. A more complete explanation will be given later 
in this paper. 

Use is made here of "densitometric level" for the purpose of com- 

July, 1938] 



paring the results obtained in the two methods of printing. The 
zero reference of densitometric level is chosen as that of an ideal film 
in which the clear portions are completely transparent, the dense 
portions completely opaque, and the recorded track is equal in width 
to the scanning slit. A perfect sound-track with the present stand- 
ardized dimensions for width of recorded track and scanning-slit 
width would have a densitometric level of 0.9 db. 

The procedure for determining the processing conditions has been 
described previously in the JOURNAL. 1 

Procedure. Modulated recordings were made on panchromatic 
film, using the standard ultraviolet optical system on an R-4 type of 

O-O I.O 

Print Dnsity--Sound-Track 

FIG. 2(B). Panchromatic sound recording: fogging 
of positive track. 

recorder, but substituting a 2-mm. No. 597 Corning filter, for the 30- 
mil No. 584 filter. 

The recordings consisted of 1000-, 6000-, and 6000-cycles modu- 
lated with 400-cycles, each of sufficient length for making output 
measurements. A frequency of 6000 cycles was used in this case 
since this is the cut-off frequency of most single-film systems for 
newsreel work. The film was then processed for picture technic by 
developing the panchromatic film in D-76 for S 1 /^ minutes at 62 F. 
producing a gamma of 0.58. The negative was then printed on 
the non-slip printer upon motion picture positive and processed for 
picture technic by developing in D-16 for 4 : /2 minutes at 65F, giv- 
ing a gamma of 2.10. 

The high-contrast prints were also made on the non-slip printer 
using a high-contrast emulsion and developing in a high-contrast 

32 J. O. BAKER [J. S. M. P. E. 

developer, Developer A, 2 for I3 l /z minutes at 65F, producing a 
gamma of 3.95. 

A frequency recording ranging from 1 to 10,000 cycles was made 
also on the panchromatic film and printed upon both the motion 
picture positive and high-contrast positive with their respective 
processings for determining the high-frequency loss. 

An unmodulated track of various widths ranging from 5 to 36 mils 
was recorded on panchromatic film and printed upon both types of 
positives for the purpose of making the ground-noise measurements. 

All output measurements were made on a calibrated film phono- 
graph and were corrected for amplifier and reproducer slit losses. 
All measurements are expressed in terms of the densitometric level. 



5 OT tt.P. PosltlT* Print (D p r 1.5) from UV sound Recording NgatlY (D n 


UT II. P. PoaltiT* Print (D s 1.15) tram DT Panohromatle Ne sa ^ 



/OO ,0*0 

FIG. 3. Panchromatic sound recording: film loss characteristics. 

Panchromatic Negative. While a number of negative densities were 
recorded, the one with a track density of 1.0 was chosen for showing 
the relative levels and image-spread cancellation, since this density 
will probably be the average that can be obtained in practice. 

For the film-loss characteristics and ground-noise measurements, 
slightly higher densities were used. The sensitometric curve is 
shown in Fig. 1. 

Motion Picture Positive. The motion picture positive stock was 
printed to various densities for determining the image-spread can- 
cellation and relative outputs. 

The sensitometric curve for the motion picture positive is shown in 
Fig. 1 and the 1000- and 6000-cycle output measurements together 
with the 400-cycle output are shown in Fig. 2(A). Fig. 2(B) shows 
how the fogging of the clear portion of the printed track varies with 
the printed track density. 

July, 1938] 



The print of film-loss characteristics was made at a density of 
1.11, and the results are shown in Fig. 3. The print for the ground- 
noise characteristics was made at a density of 1.23, and results are 
shown in Fig. 4. 

In the latter two cases, the print density was made to equal that 
of the negative density as nearly as possible. All motion picture 
positive prints were made with an ultraviolet filter in the printer. 

High-Contrast Positive. The high-contrast positives were printed 
on the non-slip printer with white light and the various results ob- 
tained are shown in the corresponding figures mentioned above for the 
motion picture positive. 

FIG. 4. Panchromatic sound recording: ground-noise 

Discussion. In Fig. 2 the motion picture positive print for a den- 
sity of 1 is approximately Q l / 2 db. below the output of a print made 
from an ultraviolet recording on sound recording positive while the 
output of the high-contrast emulsion is only l v /z db. lower than that 
attainable with a print made from a negative recorded on standard 
sound recording positive emulsion. The fog density for the motion 
picture positive at a track density of 1 is 0.35, while that of the high- 
contrast positive is only 0.08. 

Cancellation of image spread occurs over a rather wide range for 
the high-contrast emulsion, ranging from approximately 0.09 to 1.2, 
while that of the motion picture positive ranges from a print density 
of 1.0 downward. 




The film-loss characteristic of Fig. 3 shows a low-frequency output 
for the motion picture positive print of only 12 db. while the high- 
contrast low-frequency level is 5 db. The 10,000-cycle output for 
the motion picture positive is 2 db. less than that for the standard 
sound recording, while the output for the high-contrast positive at 
10,000 cycles is only l /% db. less. The ground-noise for the high-con- 
trast is considerably lower than that for the motion picture positive, 
being 19 db. lower for low values of modulation. 

The use of an inverted mask in the recorder optical system for re- 
cording a positive sound-track provides a negative sound-track when 

Negatlv* Track Density 

FIG. 5. Panchromatic sound recording: differential 
exposure through track and fog densities of negative 
(fog density = 0.34). 

printed upon the high-contrast emulsion, which could then be used 
as a negative for printing directly to the motion picture prints. 

Fig. 5 provides a ready means for determining the track fog 
density of a print for any value of recorded track density. The dif- 
ferential exposure when applied to the base line of the sensitometric 
curves will spread between the print track density (which should be 
the same as the negative track density) and the track fog density. 

Conclusions. Since the fog density of panchromatic film is approxi- 
mately 0.34 and the maximum negative track density attainable is of 
the order of 0.8 to 1.1, the difference in transmission through the dense 
and clear portions of the track is quite small. Printing this track 
upon positive film results in fogging the clear portion of the printed 


track, thereby introducing noise and reducing volume range. The 
higher the negative density, the less will be the ground-noise and the 
reduction in volume range. 

When the negative and positive sound-tracks are processed in ac- 
cordance with picture technic, the print density should be equal to 
the negative density or slightly less. With a negative track density 
of 1.0 on the panchromatic film and a print density of 1.0 on motion 
picture positive, the density of the clear portion of the printed track 
is approximately 0.35, resulting in a densitometric level for 1000 cycles 
of 12 db. and a ground-noise level of 28 db. for zero signal and 
-38 db. for a 100-per cent signal. 

Printing this same negative on a high-contrast emulsion for the 
purpose of making a dupe negative or master positive for re-recording, 
the density of the clear portion of the track is 0.08, giving a densito- 
metric level of 7 db. and a ground-noise level of 37 db. for zero 
signal, and 50 db. for a 100-per cent signal. 

While satisfactory results can be obtained from an ultraviolet re- 
cording on panchromatic film and printing directly to motion picture 
positive, they are far from ideal. The use of a high-contrast emulsion 
as an intermediate step provides means for obtaining greater volume 
range and lower ground-noise. The final release print in either case 
can not, of course, be as good as recordings made on the finer-grained 


1 BAKER, J. O., AND ROBINSON, D. H.: "Modulated High-Frequency Re- 
cording as a Means of Determining Conditions for Optimal Processing," /. Soc. 
Mot. Pict. Eng., XXX (Jan., 1938), No. 1, p. 3. 

2 BAKER, J. O.: "Recording Tests on Some Recent High-Resolution Experi- 
mental Emulsions," /. Soc. Mot. Pict. Eng., XXX (Jan., 1938), No. 1, p. 18. 


MR. FRAYNE: Why was the change made from the 584 to the 597 filter, which 
has more blue-violet? 

MR. SACHTLEBEN : For the reason that the 584 transmitted more red light than 
the 597. Of course the red could be reduced somewhat by increasing the thickness 
of the 584, but we should have to go up quite a way and suffer a loss in the ultra- 
violet. We chose the 597 to get rid of the red without such loss. 

MR. RICHTER: What is the thickness of the niters? 

MR. SACHTLEBEN: The 597 used in the newsreel system is 2 mm. thick. That 
was the minimum thickness we could use and still eliminate the red. 




Summary. An optical system has been designed and tested for use in 35-mm. 
sound reproducers. It is the slitless type, and gives a scanning image that is 0.001 
inch wide when used with an exciter lamp having a coil diameter of 0.055 inch. A 
tone lens is used to form a curved-line image of the filament of the lamp. This curved 
image is then re-imaged by a highly corrected objective lens of numerical aperture 
0.28. The objective lens has inherent curvature of field, but this curvature is compen- 
sated by the curvature of the line-image formed by the toric lens so that the final image 
is flat. The toric lens also acts as a condenser lens to throw an image of the 
filament into the objective lens. Careful tests of samples show that the final image is 
flat, straight, and of uniform width and intensity. 

The purpose of the optical system in a sound reproducer for sound 
on film is to provide a narrow bright line of light, usually 0.084 inch 
long and 0.001 inch wide, on the sound-track of the film. 

Some of the requirements of the system may be stated briefly as 
follows : 

(1) The line image must be of the proper dimensions. 

(2) The image must be as bright as possible. 

(3) No light other than the light in the image should strike the film. 

(4) The image must be straight. 

(5) The image must be fiat, so as to be in focus in the plane of the film along the 
entire length of the image. 

(6) The image should be of uniform width and of uniform intensity along its 

(7) In the plane of the film, the image must be at right angles to the direction 
of motion of the film. 

(8) Small displacements of the source should not produce changes in the in- 
tensity or dimensions of the image. 

A great variety of optical systems have been designed from time to 
time. In general, they fall into three classes: (1) The slit type, in 
which an image of the filament of the exciter lamp is formed upon a 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 22, 1938; Communication No. 670 from the Kodak Research Laboratories. 

** Eastman Kodak Co., Rochester, N. Y. 



narrow physical slit and the slit is then re-imaged by an objective 
lens upon the sound-track on the film; (2) the condenser projection 
system, similar to a lantern-slide projector, in which an objective lens 
forms an image of the condenser (and anything placed over the con- 
denser) upon the film : a physical slit is accordingly placed over the 
condenser lens; (3) the slitless type or so-called apertureless system, 
in which an image of the filament itself is formed upon the film by one 
or more lenses. 

Of these classes, the first has two serious faults : (a) If a coiled fila- 
ment is used, the illumination along the slit will not be uniform be- 
cause of the individual turns of the coil ; (b) the filament must be lo- 
cated very accurately, relatively to the optical system, in order to 

FIG. 1. Idealized perspective view of the optical system. 

place the image of the filament exactly upon the slit ; otherwise, loss 
of illumination and microphonics will result. 

The second class of optical system may be subject to microphonics 
resulting from movement of the image of the filament across the ob- 
jective lens. On the other hand, this class should give very uniform 
illumination along the length of the scanning image. 

The slitless type of optics is superior in its freedom from micro - 
phonics. The width of the scanning line, however, is not fixed by the 
optical system alone, but depends upon the size of the source and the 
distance of the source from the lens. 

An important problem in the design of high-quality sound optics 
is to obtain a flat scanning image upon the film. This problem 
arises from the fact that the simpler types of spherical objective 
lenses have the defect of curvature of field. This defect is in some sys- 


J. H. McLEOD AND F. E. ALTMAN [J. s. M. p. E. 

terns compensated for by curved slits or by curved virtual images of 
slits to make the final image flat. 

One of the features of the system herein described is the unique 
method used to obtain a flat field. Another aspect of the system is 
that it does not belong to any one of the three main classes mentioned, 
but is a mixture of (2) and (3). 

Fig. 1 illustrates the general idea of the system and Fig. 2 shows 
elevation and plan views of it. Fig. 2(B) illustrates the projection 
type of sound optics; the elevation view, Fig. 2(^4), the slitless type. 
Let us look at the elevation, Fig. 2 (A). The small cylindrical lens in 

S O.OOi" 











FIG. 2. Sound optics for 35-mm. reproducers: (.4) elevation view, 
(5) plan view. 

the condenser unit images the filament into a line at a reduction of 
18.3 times in the short dimension. This line is re-imaged upon the 
film at a reduction of 3:1 by a high-quality spherical objective. If 
the diameter of the filament coil is 0.055 inch, the final image is there- 
fore 0.001 inch thick. 

A mask covers all of the condenser unit except a narrow strip along 
the small cylinder. The width of the strip is such as to provide a 
relative aperture about twice as large as is necessary to fill the objec- 
tive lens. This allows for a vertical displacement of the filament of 
about half its diameter, up or down, without affecting the intensity 
of the light that passes through the objective. Microphonics are thus 
almost completely eliminated. 

Fig. 2(B) is a plan view of the optical system. The unique design 

July, 1938] 



of the condenser unit now becomes apparent. It is seen that the 
small cylinder, shown in cross-section in Fig. 2(A), has a curved axis. 
In this way a toric lens is produced. Its minor radius appears in Fig. 
2(A) and its major radius in Fig. 2(B). 

The major radius of the toric lens has two very important pur- 
poses: It acts in conjunction with a special window as a condenser 
lens to throw an enlarged image of the filament into the objective 
lens; and in addition, it produces a curved line image of the filament 
within the glass of the condenser unit. This curvature of the image 
is for the purpose of matching the curvature in the object space of 
the objective lens so that the final image will lie flat upon the film. 
It so happened that the curvature required for the condenser and for 
correcting the curvature of field were practically identical. 

FIG. 3. Path of a ray through a toric lens. 

A circular aperture D was placed over the condenser unit, as shown 
in Fig. 2(B), to define the length of the scanning image. 

A window was placed over the condenser unit to keep dirt away 
from the surface of the toric lens. In addition, the window is an 
aspheric lens whose inner surface is shaped to compensate for "spheri- 
cal" aberration in the condenser aspect of the toric lens. 

The objective lens consists of three simple achromatic doublets. 
The doublet on the object side collimates the light; the other two 
then bring the parallel beam to a focus upon the film. The lens is 
very highly corrected, and therefore gives excellent definition in spite 
of the high working aperture of //1. 8, or the numerical aperture of 
0.28. Incidentally, the working aperture could be increased to //1. 5, 
if desired. 

40 J. H. MCLEOD AND F. E. ALTMAN [J. S. M. p. E. 

In order to test the general idea of the optics as outlined above, a 
toric lens as described was made up. The system gave a very well 
defined image of great intensity and it lay flat in the plane of the 
film. One expected defect, however, was apparent, i. e., the width 
of the image was less at the ends than at the center. An examination 
of the first curved image formed directly by the toric lens showed 
that it, too, suffered from a falling off in width at the ends. 

The reason for the decrease in width of the line image at its ends 
was that rays from the lamp that struck the toric lens at points off 
the axis of the lens system did so at an angle 6, rather than normally 
(Fig. 3). These rays, therefore, encountered a sharper curve and 
were brought to a focus at a shorter distance and, therefore, formed 
a smaller image. 

X \ 

1 J 

FIG. 4. Section of a cylinder cut by a plane at the 
angle 6. 

The magnitude of the defect can be calculated as follows: The 
section of a complete cylinder cut by a plane is an ellipse (Fig. 4). Let 
the radius of the cylinder be r. Then the minor axis of the ellipse will 
be r. Let the major axis of the ellipse be a. Then a = r/cos 6. We 
are interested in the radius of curvature of the ellipse at the end of 
the major axis because that is the curvature that determines the 
power of the cylindrical lens for rays hitting it at the angle 6. It 
can be shown from geometry that the radius of curvature R at the 
end of the major axis of an ellipse equals r z /a. Substituting for a, we 
get R = r cos 6. Thus, the effective radius of the toric lens decreases 
as cos 6, and, therefore, the size of the image formed will be propor- 
tional to cos 6. This was found to be true experimentally in the case 
of the toric lens mentioned above. 

A new toric lens was then designed in which the minor axis was 

July, 1938] 



made greater in the proportion I/cos at points off the axis of the 
system. Fig. 5 shows the appearance of the finished lens. 

Three of these completed lenses were mounted in three finished 
optical systems and were given very careful tests. 


\ '. \ \\\\% 

FIG. 5. The toric lens. 

The optical system being tested was mounted in a jig along with a 
10-volt, 5-ampere exciter lamp placed at the proper position relative 
to the optics. The jig was then placed upon a travelling microscope, 
and the microscope was focused upon the scanning image. The 

FIG. 6. Enlarged plot of scanning image. 

microscope had a 4-mm. objective in it so that a magnification of 
about 400X was produced. A micrometer eye-piece was used in the 
microscope to measure the position of the edges of the image and 
hence the width of the scanning line. The microscope could be moved 
sidewise to bring into view any desired part of the scanning image. 

The image was found to be flat to such a high degree that it was 
scarcely possible to detect any loss of sharpness as the microscope was 


J. H. McLEOD AND F. E. ALTMAN [J. S. M. P. E. 

moved from end to end of the image. With the micrometer eye-piece 
measurements were made of the positions of the two edges of the 
image, at twenty-two positions distributed equally along the length 
of the image. Fig. 6 is a plot of these measurements taken of one of 
the systems; the straight lines were drawn 0.001 inch apart. Inspec- 
tion of Fig. 6 shows that the image was straight and of uniform width 
to a high degree of accuracy. The other two systems had images sub- 
stantially the same as that given in Fig. 6. The average widths of 
the images formed by the three systems were 0.00107 inch, 0.00104 
inch, and 0.00107 inch, respectively, and the lengths were 0.0847 
inch, 0.0852 inch, and 0.0847 inch. The correct length is 0.084 

FIG. 7. Microdensitometer traces of intensities along 
the scanning images produced by sound optical systems. 
The curves marked 1, 2, and 3 are for three sample 
systems of the type described. The one marked STD 
is for a well known system in general use. 

0.001 inch. The width of the image can, of course, be adjusted by 
placing the filament of the lamp closer to or farther from the optical 
system. For example, if the filament were moved 1 mm. farther from 
the optics, the size of the final image would be reduced by about 7 per 
cent. A microdensitometer trace showed that the uniformity of il- 
lumination remained the same when this change was made. 

The final test was to place the jig containing the optical system in 
a microdensitometer so that an enlarged image of the scanning image 
was thrown across the slit of the microdensitometer. When the stage 
of the microdensitometer was moved, it carried the optical system 
with it, and the image moved across the slit, and thus a record could 
be made of the intensity of the scanning image from one end of the 
scanning image to the other. A standard optical system of a well 
known make was tested in a similar way. An 8-mm. objective was 


used in the microdensitometer instead of the usual 16-mm. one so as 
to be certain that all of the cone of light from a point of the scanning 
image would be transmitted to the photocell. 

The curves of Fig. 7 give the results. It will be noted that the new 
systems give about 35 per cent more light than the standard system, 
as indicated by the average heights of the curves. Of this amount, 
23.5 per cent would be accounted for by the use of an//1.8 objective 
instead of the //2.0 objective used in the standard optics. Another 
6 per cent would result from the fact that the width of the scanning 
images is 0.00106 inch wide instead of 0.0010 inch. In addition, it 
was noticed that the objectives in the three new optics were almost 
completely filled with light because of the nature of the design, 
whereas in the standard the objective was not completely filled. 

The other factor to be noticed is the variation in the height of the 
curves from one end to the other. Measurements give a variation of 
=*= 11, 13, and 9 per cent for the three new systems, and 17 per 
cent for the standard one. 

To sum up, we now list the following advantages for the new 
optics : (a) Considerable tolerance in the position of the filament of 
the exciter lamp is permissible, e. ., 0.020 inch in any direction; 
(b) freedom from microphonics ; (c) excellent definition; (d) an ex- 
tremely flat and straight image ; (e) good uniformity of light-intensity 
along the length of the image and a high total intensity ; and (/) com- 
paratively low cost. 


MR. ALBERSHEIM: I should like to warn against being too optimistic with 
regard to lamp filament vibrations in such a system. While vertical vibration of 
the filament in this type of optic will not produce microphonic noise, it will shift 
the scanning-beam image up and down in a direction opposite to the filament 
vibration and therefore will modulate the signal frequency, producing flutter. 
Therefore, it is better to watch for good cushioning of the lamp despite the ab- 
sence of direct microphonics. 

MR. ALTMAN: It is true that there would be a slight motion of the scanning- 
beam in the film-gate with an extreme vertical vibration of the filament. How- 
ever, since the total optical reduction is about fifty to one, such motion should 
not be serious. 

MR. CARLSON: Mr. Altman mentioned the fact that the height of the scan- 
ning-beam could be reduced by moving the source either nearer to or farther from 
the collecting lens. It might be well to add that the height of the scanning-beam 
can be varied also by selecting a lamp having a coil diameter different from the 
one referred to in the paper. 

MR. ALTMAN: Mr. McLeod examined the uniformity of intensity with some 

44 J. H. McLEOD AND F. E. ALTMAN [J. S. M. P. E. 

longitudinal motion of the source. He moved the source enough to produce a 
6 to 8 per cent change in the height of the scanning image. No appreciable change 
in the uniformity of illumination was noted. 

MR. KELLOGG: Have you any figures, either calculated or measured, that 
show the tolerance of filament height, as limited by the tendency to produce a 
curved image on a film if it gets much below a normal level? 

MR. ALTMAN: We had not anticipated a departure from the ideal axial posi- 
tion, which I imagine is what you mean would cause a curvature. There was a 
suggestion of slight curvature in the findings of Mr. McLeod. Whether or not 
that was due to a slight defect in the pressing or caused by some displacement I 
would not know. 

MR. COOK: How do you form a lens as complicated as that? 

MR. ALTMAN: It is a molded lens. The die is polished so that an optical sur- 
face results. The making of the die can be visualized by imagining a piano wire 
wrapped around a small cylinder, and this used as a pattern for the die. It was 
found necessary to vary the diameter of the piano wire along its length to secure 
uniform width of image of the filament. 

MR. FRIEDL: Do you find in this system any secondary images, caused by 
reflection within the glass of the exciter lamp? 

MR. ALTMAN: There is in the system a mask. The focal length of the ana- 
morphote in its strong meridian is about 0.8 mm., and since we wish to flood the 
imaging objective with light at about //5.4, you would have to have an aperture 
in that meridian of only 0.8/5.4, which would be about 0.15 mm. That does re- 
quire, then, a small mask with a slit 0.15 or 0.20 mm. along the strong meridian 
of the pressing. The diffraction, or scattered light, from the edges of the mask 
might cause some secondary image. 

MR. MCLEOD: If the axis of the exciter lamp is perpendicular to the axis of 
the optical system, as it is in practice, the reflected image in the glass is directly 
behind the filament and is hidden by the filament. However, it has been found 
that if the lamp is displaced a considerable distance above or below its proper 
position, a weak image is formed above or below the main image. The displace- 
ment to produce this, however, has to be greater than is normally encountered. 

MR. FRIEDL: Do you find that so-called azimuth variation is more critical in 
this type of system? In the system with the mechanical slit, the slit is held 
in fixed relation with respect to the optical scanning beam, and that determines 
the azimuth with respect to the position of the filament; whereas in this case, 
I am wondering whether or not the tilt of the filament axis may not introduce an 
azimuth loss or scanning loss, as a function of the tilt. 

MR. ALTMAN: Each and every point on the filament is imaged as a line on the 
film, and the azimuth of the line is determined solely by the azimuth of the press- 
ing or cylinder. The total image on the film is the net effect of all the lines imaged 
from all the points on the filament. 

If the filament is tilted it will not change in the slightest degree the azimuth of 
the final image but will increase somewhat the height of the image. 

MR. FRIEDL : That is the same effect as is due to misalignment in a mechani- 
cal system. The effect of the azimuth is the same as having a slit as wide as the 
two corners. 

MR. ALTMAN: That is true. 


MR. FRIEDL: And the filament sag would cause a very similar effect. 

MR. ALTMAN: That is right. The particular lamp we have suggested is well 
suited because it has a rather large diameter of filament and a rather short length. 
A given angular tip therefore produces less spread of the image than would a simi- 
lar angular tip with a long slender filament. 

MR. KELLOGG : I believe that I see the answer to the question I asked a few 
minutes ago in reference to the effect of changing the lamp height ; the conditions 
of focal length and focus position that give you a beam of uniform width are 
identical with the conditions for relative immunity to curvature resulting from 
change in lamp height. 

MR. MCLEOD: We agree that Mr. Kellogg's remark is an exact statement of 
the truth regarding the absence of curvature when the height of the lamp is 
changed. The toric lens is designed to give a line image of uniform width. That 
means that the magnification is the same at the center as at the ends of the line. 
Since the magnification is the same, a given displacement of the source up or down 
will cause a displacement of the line up or down that will be the same at the cen- 
ter as at the ends. In other words, the plane of the curved image (which is hori- 
zontal) will remain parallel to itself if the source is moved up or down. It is true 
that as viewed from the objective the curved line will appear straight when the 
plane of the curve passes through the center of the objective, but when the plane 
moves above or below the center of the objective lens the curved line will appear 
to be slightly curved. A slightly curved image would be produced. However, 
since the vertical displacement of the curved image is Vis the displacement of the 
source, and this in turn is reduced to Va size, the curvature in the final image on 
the film would be too small to measure. 


Summary. Push-pull recording on film is accomplished by means of a double 
light-valve having four ribbons. Distortions introduced by the recording medium that 
are represented by second-order harmonics balance out in reproducing, as do also the 
frequencies introduced by the action of the noise-reduction system. As a result, push- 
pull recording not only eliminates certain defects of conventional recording, but per- 
mits the application of new technics that allow further extension of the volume range 
and improvement in the naturalness in the final product. 

The use of the push-pull principle in transmission systems is well 
known as a means by which certain distortions introduced by the 
transmitting devices are balanced out. These are distortions caused 
by the introduction of second-order harmonics and effects that occur 
simultaneously in both sides of the push-pull system, but not in push- 
pull relationship. This principle has been applied to recording sound 
on film by recording two adjacent tracks 180 degrees out of phase 
with each other. x The two tracks are scanned in reproducing so that 
the light transmitted through the individual tracks falls separately 
upon two photoelectric surfaces connected to amplifiers in such 
manner that the resultant voltage developed is proportional to the 
difference in transmission of the two tracks. In this manner the 
push-pull principle is employed to balance out certain distortions 
that otherwise would be reproduced. These are referred to in the 
following as "unwanted components." 

In order to understand better the value of push-pull recording, we 
shall classify here the various sources of distortion ordinarily en- 
countered in conventional recording. The exposure characteristics 
of the light- valve have already been pointed out, 2 and it was shown 
that pure sine-wave modulation by the light-valve does not always 
result in a pure sine-wave on the film, but rather, a complex wave 
with considerable second harmonic in the higher frequencies. This 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 20, 1938. 

** Electrical Research Products, Inc., Los Angeles, Calif. 


is the direct result of the velocity with which the film moves. Ref- 
erence to Appendix A illustrates how the unwanted components thus 
introduced are eliminated in push-pull recording. A second effect of 
the film velocity is intermodulation between the high and low fre- 
quencies. When the modulation is sufficiently high that overload 
occurs, both even and odd harmonics are impressed upon the film 
along with other products of the overload that are of such nature as 
to be largely eliminated by the push-pull arrangement. 

Another source of distortion may be introduced in the development 
and printing process. It will be recalled 3 that if the modulation of the 
negative is entirely confined to the straight-line portion of the nega- 
tive H&D curve, and the printer point is selected to confine the 
modulation on the print to a similar part of the print characteristic, 
the true overall gamma being kept at unity, no unwanted components 
are introduced by the processing. However, if the gamma is per- 
mitted to depart from unity harmonics are introduced ; or, the gamma 
being held at unity, an improper selection of negative or print density 
will result similarly in the introduction of harmonics, as shown by 
reference to Appendix B. The cancellation of harmonics in this 
case by the push-pull process is identical to that brought about by the 
use of the push-pull stage in amplifiers where the unwanted com- 
ponents are introduced by the curvature of the operating character- 
istic of the vacuum tubes. 

Another form of unwanted component is introduced in film record- 
ing by the process of noise reduction. 4 In this case, in addition to 
the signal recorded upon the film, some low-frequency rectified com- 
ponents transmitted through the noise-reduction filter are intro- 
duced also, the effect being sometimes known as "shutter bump." 
The existence of this effect has restricted the application of noise- 
reduction principles. In push-pull recording, while the signal is 
recorded on the two tracks 180 degrees out of phase, the noise-reduc- 
tion modulation is in phase on the two tracks. Thus, these unwanted 
noise-reduction components being recorded in phase, are cancelled 
out when the tracks are reproduced in push-pull. This makes pos- 
sible a much faster-operating noise-reduction mechanism which, in 
turn, permits greater noise reduction. The faster type of noise re- 
duction makes possible the use of a much smaller "margin" which, in 
turn, tends to reduce the "hush-hush" effect that is quite noticeable 
in single-track recordings of some types of recorded sounds. While 
push-pull recording is instrumental in largely reducing the types of 

48 J. G. FRAYNE AND H. C. SILENT [j. s. M. p. E. 

distortion listed in previous classifications, perhaps its most spec- 
tacular use has been in permitting much more effective use of noise 
reduction or what amounts to a much greater signal-to-noise ratio 
of the recording medium. 

Reference has been made to the intermodulation effects due to film 
velocity. This intermodulation results in amplitude variations of 
a high frequency recorded simultaneously with a low frequency, the 
amplitude of the high frequency being reduced when the light-valve 
ribbons open under the action of the low frequency. Since in push- 
pull recording one half of the valve is at its maximum opening when 
the other half is at its minimum opening, the amplitude variations of 
the high frequency are opposite on the two halves of the push-pull 
track. Thus they tend to offset each other when the track is repro- 
duced. Variations that might be as great as 20 per cent on a single 
track are reduced to only 1 x /4 per cent on the push-pull track. 

Under certain conditions of processing the transmission-exposure 
characteristic may depart from a straight line. If the departure is at 
one end only, it introduces second-order harmonics which are balanced 
out in the reproduction of push-pull records. This form of depar- 
ture also results in volume distortion and intermodulation which are, 
in turn, considerably reduced in push-pull. When the departure of 
the transmission-exposure characteristic occurs at both ends, i. e., is 
essentially symmetrical, odd-order harmonics are introduced which 
can not be balanced out, and the volume distortion and intermodula- 
tion also are not reduced by push-pull. Since the "delta db." test 
reveals the nature of the departure of the transmission -exposure 
characteristic, 5 it provides a means for readily checking the value of 
push-pull recording in reducing this type of distortion, and for de- 
termining the amount of noise reduction that may safely be applied. 
The latter is usually about 14 db. in good commercial processing. 

An incidental advantage of push-pull recording is its adaptability 
to certain forms of pre- and post-equalization recently proposed by 
Douglas Shearer of the Metro -Goldwyn-Mayer Studios. Since the 
noise-reduction action is recorded in phase on both halves of the 
push-pull track, any low-frequency components of this action balance 
out and are not reproduced as sound. Even when considerable over- 
emphasis of the low frequencies is given ih reproduction by means of 
equalization the noise-reduction action or "shutter bump" is still 
inaudible. Therefore, by attenuating the low frequencies in re- 
cording and introducing an equivalent gain in reproducing, several 

July, 1938] 



incidental improvements are obtained without any sacrifice in qual- 
ity. The reduced amplitude of recorded low frequencies reduces 
still further the intermodulation between high and low frequencies. 
There is also a reduction of modulation of the ground-noise by low 

FIG. 1. Four-ribbon push-pull light-valve. 

frequencies of high amplitude, since their amplitude is kept low at all 
times. This results in a greatly improved tonal quality or purity in 
this register. Since the low frequencies are reproduced through an 
equalizer that reestablishes their relative levels, the high frequencies 

FIG. 2. Light-valve monitoring by means of quartz rods. 

of the signal and of the ground-noise are reproduced through some 
attenuation. The result is a reduction in apparent ground-noise, 
with an improvement in usable volume range of at least 5 db. and a 
complete elimination of "hush-hush" on even the most difficult re- 
cording material. 


J. G. FRAYNE AND H. C. SILENT [j. S. M. P. E. 


(a) Recording Channel. The microphone, recording amplifier, and 
mixing equipment for push-pull recording are the same as for standard 
recording. The noise-reduction unit is provided with a special ad- 
justment producing a faster time of operation (of the order of 6 
milliseconds). The noise-reduction current is fed to the light-valve 
through a potentiometer to balance the current in each half of the 
light- valve, thus insuring the same noise reduction on each track. 

(b) Push-Pull Light-Valve. The light-valve for push-pull re- 
cording is essentially two valves, being equipped with four ribbons 
instead of the customary two. A valve with similar modulating 





FIG. 3. 

Light-valve monitoring by means of partial re- 
flector plate. 

structure is described in a paper by E. C. Manderfeld. 6 A photograph 
of the electromagnet type of valve is shown in Fig. 1. 

The normal spacing of the light-valve without bias is 1.4 mils. In 
order to achieve the maximum noise reduction possible, a high ratio 
of maximum to minimum light-valve spacing, under the control of 
the noise-reduction circuit, is desirable. Accordingly, the noise- 
reduction device has been designed to provide a reverse bias on very 
loud signals, thereby causing the light-valve to open to 2.0 mils. 
Noise-reduction settings of 14 db. are entirely satisfactory, and under 
very carefully controlled conditions excellent recordings have been 
obtained with as much as 20 db. of noise reduction. Because of the 
fast operation of the noise-reduction system made feasible by push- 
pull recording, considerably reduced margin settings are possible, as 

July, 1938] 



little as 1 to 2 db. being commonly used. This results in reduced 
"breathing" of the ground-noise or "hush-hush." 

(c) Push-Pull Photoelectric Cell Monitoring. Fig. 2 shows the 
arrangement of the valve to provide photoelectric cell monitoring. 
It will also be noted that two small rods extend from each side of the 
valve and pass underneath each pair of ribbons. These are quartz 
rods which deflect a small fraction of the modulated light from each 
side of the valve. At the same time the mount for these rods serves 






j\ . 

100 MIL 





' " 












1 - 





i i . 

200 MIL 






FIG. 4. Dimensions of push-pull positive sound- 

provide a septum between the two tracks. Fig. 2 shows also how 
le light transmitted through the rods is deflected in turn to individ- 
ial photoelectric cells, the output of the cells being connected in 
push-pull to the monitoring amplifier. Another monitoring arrange- 
ment recently developed is shown in ig. 3. This consists of a thin 
unsilvered flat glass plate mounted at 45 degrees to the recording 
beam, and deflecting a small portion of the entire modulated light 
through a suitable lens system, which in turn produces upon the 

52 J. G. PRAYNE AND H. C. SlLENT [J. S. M. P. E. 

cathodes of a double-anode photoelectric cell two enlarged images of 
the recording slits. The monitoring system may be used for standard 
or push-pull recording without any change other than operating a key. 
(d) Optical System. The optical system used in push-pull record- 
ing is essentially the same as that used previously with standard re- 
cording. Because of the double light-valve, it is necessary to use a 
slightly longer filament in the exciting lamp. The objective lens is 
of the type previously described, 7 but has been specially designed to 
give a 4 : 1 reduction of the light-valve aperture at the film plane. 
This results in the standard track width of 100 mils, the center of the 











FIG. 5. Push-pull reproducer optical systems. 

track being 54 mils from the inside edge of the sprocket-holes. The 
use of the 4:1 reduction makes it possible to use a mean light-valve 
spacing up to 2 mils without exceeding the V2-mil image height which 
has been standard practice with 1-mil light-valves and 2:1 lens re- 
duction. The dimensions of the track are shown in Fig. 4. For origi- 
nal recording from which to re-record, and where no interference 
between sound and picture is involved, the Metro -Goldwyn-Mayer 
Studios have produced push-pull sound-tracks through the original 
2 :1 lens. This results in a track 200 mils wide, having a signal-to- 
noise ratio 3 db. higher than that of the 100-mil track. The dimen- 
sions of this track are shown also in Fig. 4. 

July, 1938] 



In general, the film-processing practices and controls that are used 
in processing standard variable-density track are followed for push- 
pull track. Because of the balancing out of certain distortion com- 
ponents it is possible to permit deviations from the customary prac- 
tices without having to sacrifice the standard of quality. However, 
it is not possible to obtain all of the other benefits of push-pull re- 






FIG. 6. 

Schematic diagrams of circuits for 
push-pull reproducing. 

cording when these deviations are permitted. Thus, if no more than 
the usual amount of noise reduction is used, say, 8 db., there exists 
considerable latitude in print density and overall gamma over which 
a satisfactory product is obtainable. If, on the other hand, full 
benefit is taken of the higher noise reduction possible, then film 
processing is no less critical than formerly. Under this condition devi- 
ations in overall gamma result in volume distortion of the reproduced 
sound, and incorrect print density frequently produces both volume 
distortion and intermodulation of the recorded 'sounds, both of which 
may be practically non-existent at lower values of noise reduction. 

54 J. G. FRAYNE AND H. C. SILENT [j. s. M. P. E. 


In order to reproduce two push-pull sound-tracks it is necessary 
to provide either two individual photocells or a special photocell 
having two cathode surfaces and a double anode, which amounts to 
placing two individual photocell units within one envelope. An op- 
tical system must be provided to collect the light from each sound- 
track onto the proper cathode surface. The image-scanning method 
of reproduction lends itself very readily to push-pull reproduction and 
has been used quite extensively in re-recording and in theater repro- 
ducers. Such an optical system combined with a double photocell 
and also with the special double anode photocell is shown in Fig. 5. 
In Fig. 6 is shown the method whereby either system is coupled 
through resistance or transformer to the amplifier. The key shown 
in the figure is used to switch the system from push-pull reproduction 
to standard single-track reproduction, this being the only change 
necessary to play either type of track interchangeably. Where a 
push-pull track width of 200 mils is used, it is necessary to provide 
additional means of switching from push-pull to standard, since the 
center-lines of the two tracks are different. 

Considerable study has been necessary to determine the effects of 
unbalance between the two halves of the push-pull tracks. One of 
the factors contributing to this unbalance is weave. By proper 
assignment of tolerances at various steps in the overall system, it 
appears possible to permit a weave of approximately =*= 5 mils in the 
reproduced sound-track without encountering appreciable degrada- 
tion. In order to arrive at this permissible value of weave, studies 
of movement of film in recorders, printers, and projectors were made. 
It was found that the weave in the recorder could be held to 1 mil 
by the addition of a guide-roller above the main recording sprocket 
in the standard Western Electric film recorder. The printer weave 
that might be designated more properly as displacement of track 
position was found to be approximately 2 mils from the mean 
position. This may be attributed to the fact that in the regular 
printer the film at present is guided by one set of sprocket teeth and 
the width of the sprocket tooth at the base is 4 mils less than the 
sprocket-hole dimension. It was not possible to study the amount 
of weave that may be present in all types of projectors, but it was 
found that in certain well maintained machines the weave intro- 
duced was of the order of ==2 mils. Since in all probability these in- 
dividual weaves will rarely be all in the same direction at the same 


time, the resultant weave will seldom amount to the ==5-mil toler- 
ance permitted by the scanning system. 

(a) Track Balance. The improvement to be obtained from push- 
pull recording by the cancellation of distortion may be realized fully 
only when the outputs from the individual photocells in the repro- 
ducer are equal, i. e., in balance. Differences in sensitivity of the 
translating devices or in the modulation of the two tracks will neces- 
sarily mean that instead of complete cancellation of unwanted com- 
ponents, residuals of these components will be present to some extent. 
In considering the various elements that contribute to an overall 
balance of the two push-pull tracks, the following factors may be 

(1) Uniformity of illumination of the exposing beam in recording, 

(2) Equal sensitivity of the two component valves. 

(3) Uniformity of illumination of the printer light. 

(4) Uniformity of illumination of the reproducer scanning beam. 

(5) Equality of sensitivity of cells and associated coupling circuits in repro- 

Contrary to the general impression, the balance of the tracks is not 
affected by changes that may occur in valve spacing so long as the 
valve sensitivity remains unchanged. This assumes that such 
change of spacing does not cause one-half of the track to assume a non- 
linearity of characteristic not already present. This is best under- 
stood by reference to Appendix C. 

With regard to the first three items mentioned above, the illumi- 
nation of the exposing beam can be kept within close limits by cor- 
rect adjustment of the exciting lamp with respect to the light-valve 
apertures. It has been found that the coiled filament type of lamp 
generally used is very uniform in illumination across the useful 
length of the filament. The sensitivity of the two valves can easily 
be adjusted within x /2 db., and will continue to remain balanced to 
this extent unless severely abused in the recording process. A study 
made of several printers indicated that the variation of illumination 
across the printer aperture in a commercial printer probably intro- 
duces the greatest possibility of unbalance between the tracks. The 
net unbalance in output resulting from variations in negative and 
positive density, from inequality in light-valve sensitivity, and from 
variation in printer illumination, has been found to amount to a 
maximum of about 2.5 db. 



In reproducing circuits involving the use of two individual photo- 
electric cells, these may be selected having a sensitivity unbalance of 
not more than 1 db., and it has been found possible to produce a 
double photocell having an inherent unbalance of the same order of 
magnitude. Thus a maximum of about 3.5 db. is the most that may 
be expected in the unbalance of two push-pull tracks when due pre- 
cautions have been taken to see that the various elements are lined 
up with the degree of accuracy found feasible under studio conditions. 





- 8 









FIG. 7. 

Effect of unbalance between sides in push- 
pull system. 

In order to appreciate what the effect of unbalance between the two 
tracks means to the suppression of unwanted components, the mathe- 
matical analysis shown in Appendix D has been made, the graphical 
results of which are shown in Fig. 7. The curves show that a differ- 
ence in sensitivity of 3 db. results in the reduction of the wanted com- 
ponents by about 1.5 db., but suppresses the second-order distortion 
components by about 17 db. ; this amount of suppression to be added, 
of course, to the amount by which they are already attenuated in the 
film modulation. It has been shown 1 that in single-track light- valve 
recording in which the image height is 0.5 mil, the second harmonic 


at 4000 cycles is 19.5 db. below the fundamental. Additional sup- 
pression of only 15.5 db. would reduce this to a total of 35 db., corre- 
sponding to 1.8 per cent of second harmonic. Since the third har- 
monic has been shown to be negligible in the recording range, we thus 
see that the push-pull recording essentially eliminates the unwanted 
components that are present in standard light-valve recording. It 
will be recalled that in this process a maximum spacing of 2 mils is 
permitted, but when this is associated with the 4 : 1 lens reduction, the 
image height is still retained at the 0.5-mil value which has been more 
or less the practice in standard recording. The next principal source 
of harmonics is introduced in the film processing, and experience has 
shown that if the overall gamma is not permitted to vary more than 
20 per cent from the mean value of unity, the second harmonic will 
not exceed more than 5.0 per cent of the fundamental. If we add 
this to the ribbon-velocity components and assume the 15.5-db. sup- 
pression, we arrive at a total suppression at 4000 cycles of 31.5 db. 


In the preceding discussion on the degree of balance to be expected 
in push-pull recording, it has been assumed that no special means was 
to be used to achieve better balance than could be accomplished by 
carefully lining up the equipment and taking all necessary precautions 
in recording and reproducing to see that no unnecessary unbalance 
is introduced. However, it is quite possible to balance the output 
of the two photoelectric cells either by reducing the light-flux of the 
scanning beam on the cell showing the greatest output, or by altering 
the potential of the cell anodes in such manner as to balance their 
outputs more effectively. With either of these methods it has been 
found possible to suppress the unwanted components as much as 
30 db., which is considerably more than is necessary. 


A cause of unbalance that has not been discussed hitherto is mis- 
alignment of the images on the two tracks. It will be recalled that 
the two apertures in the light-valve pole-piece are separated by a 
considerable distance and that the two recording beams passing 
through these apertures are brought into line by the use of refractor 
plates. An analysis has been made to determine what the effect of 
alignment is upon the passage of the wanted and the suppression of 
the unwanted components. The mathematical analysis is indicated 


J. G. FRAYNE AND H. C. SILENT [J. s. M. P. E. 

<M O 


July, 1938] 



in Appendix E, while in Fig. 8 is shown the loss of wanted signal for 
frequencies up to 9000 cycles, and in Fig. 9 is shown the degree of sup- 
pression of the unwanted components for misalignment values vary- 
ing from 0.2 mil to 1 mil. It will be noted that the effects are neg- 
ligible for misalignment at the film of less than 0.2 mil. Due to the 
use of the 4 : 1 reducing lens, misalignment of that amount corresponds 
to effective misalignment of 0.8 mil at the light-valve. In practice 
it has been found quite feasible to make alignment adjustments 
within a very small fraction of this requirement. 


It has been shown that the principal distortions in light-valve 
recording, such as result from ribbon velocity effect, light-valve 





*% -30 







5 35 
















z -40 






< -45 


, / 







i , 



.30 .40 .50 .60 .70 .80 .90 


FIG. 10. Comparison of second-harmonic distortion : 
single track vs. push-pull track. 

overload, and errors in film processing, have been materially reduced 
by the push-pull method. In addition, the low-frequency noise- 
reduction components and certain other extraneous components of 
accidental overload of the light-valve in regular recording are elimi- 
nated in the push-pull process, since they are recorded in phase upon 
the two component tracks. This makes possible the use of increased 
noise reduction, up to 14 db. being regarded as commercially prac- 
ticable. In reproduction no trouble has been experienced from nor- 
mal weaving of the sound-tracks. It has been shown that the degree 
of unbalance that may be introduced in the output of the two tracks 
arising from errors of operation and other discrepancies introduced 

60 J. G. FRAYNE AND H. C. SILENT [J. S. M. p. E. 

in the overall process is sufficient to suppress the unwanted com- 
ponents more than the 15 db. believed to be sufficient. Further 
improvement has been made possible by balancing devices in 
the reproducing mechanism, where the utmost is required for re- 
recording purposes. Additional advantages can be obtained by com- 
bining pre- and post-equalization with push-pull, thereby achieving 
greater signal-to-noise ratio, better tonal quality of the low fre- 
quencies, and complete elimination of "hush-hush." 

In the practical operation of push-pull systems in the studios, the 
two qualities that appeal most to the recording engineer are the ad- 
ditional noise reduction made possible by the method and the elimi- 
nation of the harsh quality that has hitherto been characteristic of 
light-valve overload. The method also permits considerable reduc- 
tion in the modulation of the light-valve for low input sounds which in 
the past would have been masked by the background noise. This 
permits more natural recording of the volume range without raising 
the low signal or depressing the high signals; in fact, for the great 
bulk of recorded material, such as dialog, little mixing is necessary 
with the push-pull method outlined here. 

At the present time the use of push-pull recording is limited to origi- 
nal recording, since comparatively few theaters are as yet equipped 
to play push-pull track. However, a definite gain is obtained in 
recording from this type of track to the standard single track, com- 
pared to re-recording from standard to standard track. 


1 MILLIARD, J. K.: "Push-Pull Recording," /. Soc. Mot. Pict. Eng., XXX 
(Feb., 1938), No. 2, p. 156. 

CBCCARINI, O. O. : "Theoretical Notes on the Push-Pull Method of Record 
ing Sound," /. Soc. Mot. Pict. Eng., XXX (Feb., 1938), No. 2, p. 162. 

2 SHEA, T. E., HERRIOTT, W., AND GOEHNER, W. R.: "The Principles of the 
Light-Valve," J. Soc. Mot. Pict. Eng., XVIII (June, 1932), No. 6, p. 697. 

3 MACKENZIE, D.: "Straight Line and Toe Records with the Light- Valve," 
/. Soc. Mot. Pict. Eng., XVII (Aug., 1931), No. 2, p. 172. 

4 FRAYNE, J. G., AND SILENT, H. C.: "Western Electric Noiseless Recording," 
/. Soc. Mot. Pict. Eng., XVIII (May, 1932), No. 5, p. 551. 

6 ALBIN, F. G.: "A Dynamic Check on the Processing of Film for Sound 
Records," J. Soc. Mot. Pict. Eng., XXV (Aug., 1935), No. 2, p. 161. 

6 MANDERFELD, E. C.: "Permanent-Magnet Four-Ribbon Light-Valve for 
Portable Push-Pull Recording," presented at the Spring, 1938, Meeting at Wash- 
ington, D. C.; to be published in a forthcoming issue. 

7 HERRIOTT, W.: "A Method of Measuring Axial Chromatic Aberration in an 
Objective Lens," /. Soc. Mot. Pict. Eng., XX (April, 1933), No. 4, p. 323. 


FOSTER, L. V., AND HERRIOTT, W. : "Recent Optical Improvements in 
Sound-Film Recording Equipment," /. Soc. Mot. Pict. Eng., XXIII (Sept., 1934), 
No. 3, p. 167. 


The exposure impressed upon moving film by a two-ribbon valve is given by the 
equation : 

, 4v r fbw\ aw . , i/. /2bw\ . 2aw _ ... 

d = 2a + I ji ^ j cos sin wt + l Aj* ^ J sm cos 2 wt + l /tfi- 

/3fcw\ 3aw . "I 

- ) cos - sm 3 wt + . . . (7) 

V v / r J 

This may be written as : 

e } = A + 5 sin wt + Ccos 2 wt + > sin 3 wt + . . . (2) 

where ^4,5, C, D correspond to the coefficients of the time function above. If 
eq. 2 represents the wave-form on one track, the wave-form on the track 180 de- 
grees out of phase is 

e 2 = A 4- B sin (wt - 180) + Ccos 2(wt - 180) + D sin 3(wt - 180) (3) 

On the print, for correct development, the transmission wave-forms will corre- 
spond to the above. Hence we may express the resultant wave-form, when the 
two tracks are correctly reproduced in push-pull, as the difference of the above. 
Thus the output 

e = ei e-i = 2 B sin wt + 2 D sin 3 wt + . . . (4) 

all even harmonics cancelling out. 


The relation between print transmission and negative exposure for film process- 
ing where the gamma is other than unity is: 

Ti = K(l + b sin w>/) 7 -o) 

Where T = print transmission. 

K = a constant. 

b = film modulation. 

7 = overall gamma of developing process. 


This reduces to 

cos 2 wt _ 7 - 2) 63 sin 3 

62 J. G. FRAYNE AND H. C. SILENT [j. s. M. p. E. 

which may be written as 

T } = K[a + bsmwt c cos 2 wt d sin 3 wt] 

As in appendix A\ a similar wave-form 180 degrees out of phase on the second 
push-pull track will result in complete cancellation of the second-harmonic term. 
An illustration of the measured cancellation of second harmonics over a wide 
range of prints density is shown in Fig. 10. 


The sample equation of exposure for the light-valve is : 

e\ = a -\- c sin wt 
where a = normal spacing of ribbons and c = amplitude of ribbon movement. 

Assume that the second valve in a four-ribbon valve is spaced ma units, and 
that its sensitivity is the same as first valve. Then the exposure through valve 
No. 2 is e 2 = ma + c sin wt. 

Now on the print the transmission of track No. 1 is TI = k(a -\- c sin wt) and 
that of track No. 2 is !T 2 = k(ma + c sin wt}. The voltage developed by each 
track is thus kc sin wt and is independent of m. This assumes that m is of such 
value that the resultant exposure in valve No. 2 does not bring out a photographic 
unbalance in the modulation of the two tracks. 


Assuming that equal sinusoidal signals are recorded on both tracks, the voltage 
impressed upon the grid of the first amplifier tube derived from track No. 1 is: 

EI = b sin wt + c sin 2 wt 
Similarly for track No. 2 

EI = nb sin wt nc sin 2 w 

where n is the sensitivity ratio of the translating device. The resultant voltage is: 
E = b( 1 + n) sin wt + c ( 1 - w) sin 2 wt 

The output of a push-pull reproducing device thus unbalanced relatively to that 
of a balanced system is: 

db. = 20 log 

The corresponding function for the second harmonic represents suppression of 
that component, and is expressed as: 

db. = 20 log 

The output of second harmonic relative to the fundamental for any degree 
of unbalance of the translating devices is : 

db. = 20 log -^-2 + 20 log c . 
1 ~\~ n o 



Track Misalignment. Assume k = linear displacement on the film between 
corresponding points of the signals, and v the speed of the film in reproduction. 
The voltages impressed on the grid from tracks No. 1 and No. 2 are, respectively, 

E\ = a sin wt 
E 2 = a sin ( wt J 

wk . wk 

= a sm wt cos a cos wt sin 

V V 

E = EI -f E-2 = a 1 1 + cos ) sin wt a s'n cos wt 

\ V / V 

This reduces to 

E = 2a cos - sin (wt 0) 


/ . wk \ 
/ sin \ 

= tan- 1 a I _ 

wk I 

\ 1+ COS T/ 

The loss of wanted signal is 

db. = -20 log -^ cos 0/2 

= -20 log cos 0/2 

The voltages of the unwanted signal from each track are similar to the above. 
Their resultant, however, is the difference rather than the sum of the individual 

The amplitude of the unwanted signal becomes E 2a sin 0/2. The suppres- 
sion is db. = 20 log sin 0/2. 


MR. DAY: Is this suppression of noise or "hush-hush" considered a novelty? 
I demonstrated this principle in 1930 and 1931. 

MR. FRAYNE: Post-equalization is well known. It has been used com- 
mercially in hill-and-dale recording for about seven or eight years and experi- 
mentally for a considerably longer period. It is possible to find many things 
that have been done in years gone by that have not been followed up, or did not 
originally work well because of some difficulties at the time. 

The form of equalization used here is not that used in the hill-and-dale method. 
This particular type was developed by Douglas Shearer, of M. G. M., and is a 
peculiar form of equalization which reduces not only the film noise but also the 
"breathing" or "hush-hush" effects. 


MR. DAY: I believe my organization put out the first sound-on-film 16-mm. 
projector, and, perhaps foolishly, we used the light from the projection lamp for 
exciting the photoelectric cell. Naturally we had a great deal of noise, so we used 
the same arrangement that you showed today, with two photoelectric cells buck- 
ing each other. Into the one cell we put a beam of light that had only noise in it, 
and into the other a beam modulated by both noise and sound. We had very 
satisfactory sound by that arrangement, and found that neutralizing by two cells 
worked very well, but we had quite a little difficulty in magnetic elimination 
through transformer coils. 

MR. KELLOGG: I did not quite understand why the push-pull system makes 
it possible to get better results out of pre-equalization than you could anyhow. 
Am I correct in assuming that the pre-equalization is essentially what is shown 
in Mr. Friedl's paper? If so, why was that particular form chosen? 

MR. FRAYNE: The reason why push-pull is desirable is that the noise-reduc- 
tion frequencies, which I spoke of as unwanted components, being in phase on 
both sides of the track, are relatively low-frequency effects. When you raise the 
low frequencies 12 db. to bring up the low end in the post-equalization charac- 
teristic, you bring up the unwanted components by 12 db. ; to a point where, in 
some kinds of recording, especially of pianos or drums, they would be above the 
desirable level. The cancellation that the push-pull system offers is very desir- 
able in getting rid of those frequencies. 

The particular curve was arrived at by considering the energy distribution in 
both speech and music, film noise, and ear sensitivity, and interrelating these in 
such a manner as to obtain the best possible signal-to-noise ratio. This results 
in practically eliminating the "hush-hush" and other effects resulting from high- 
amplitude low frequencies. 

MR. KELLOGG: In other words, the equalization is more or less complemen- 
tary to your observed or experienced spectral distribution. 

MR. FRAYNE : More or less. 


The recent publication 1 of the "Revision of SMPE Standards Pro- 
posed for Adoption by the Society" summarizes the activities of the 
Standards Committee for the past two or three years. These drawings 
have all received initial approval and final approval by the Com- 
mittee and are referred to the Board of Governors of the Society for 

Unfavorable comments have been received in regard to the sound- 
track dimensions both for 35-mm. and 16-mm. film. In the opinion 
of the Chairman of the Committee these comments justify withhold- 
ing adoption of these two standards until further study is undertaken. 

There have been very few comments on any other drawings and it is 
recommended that all other drawings be adopted by the Society.** 

The uncompleted items at present under consideration are as follows : 

(1} A study of the best dimensions for standard cores for cine film, being 
made by P. H. Arnold. 

(2) Further consideration of all the dimensions for 35-mm. and 16-mm. 

(5) Drawings for sprockets for 16-mm. sound-film. These may depend, to a 
certain extent, upon possible modifications of the sound-track dimensions. 

(4) Revision of the standard release print to correspond with the revisions 
made by the Academy. 

(5) Review and possible revision of the glossary of technical terms. 

(6) Carrying out of actual tests of the new sprocket perforation of 35-mm. 
film, which, it is hoped, will displace the old Bell & Howell perforation. 

Two punches and dies have been constructed in accordance with the 
specifications originally outlined by Howell and Dubray, 2 and another 
punch has been constructed by the Agfa Ansco Corporation using the 
same radius at the corner as the present SMPE perforation. Tests 
have been made, and further tests are under way, comparing these 
two types of perforation both for breakdown in the projection ma- 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 22, 1938. 

** Subsequently to the preparation of this report, action on the proposed re- 
vision of the standards was taken by the Board of Governors (April 24, 1938), 
all the proposals being validated as SMPE Standards with the exception of 
DS35-7-1 and DSsl6-7-l, relating to 35-mm. and 16-mm. sound-tracks. 



chine and for steadiness in various types of cameras. Preliminary 
tests give some indication that the Howell and Dubray perforation 
is not quite as good as the SMPE perforation for durability in pro- 
jection, although it is considerably better than the Bell & Howell 
perforation. Tests also indicate that in some cameras the positioning 
of the new perforation is exactly as good as with the Bell & Howell 
perforation, but that in other cameras it is not quite as good. These 
two points will have to be established definitely before a decision 
can be made. 


1 "Revision of SMPE Standards Proposed for Adoption by the Society," 
/. Soc. Mot. Pict. Eng., XXX (March, 1938), No. 3, p. 249. 

2 Report of the Sub-Committee on Perforation Standards, J. Soc. Mot. Pict. 
Eng., XXIX (Oct., 1937), No. 4, p. 376. 


E. K. CARVER, Chairman 







Summary. Advantages stated to be obtained by adjusting foxing baths and wash- 
water to the isoelectric point of gelatin have been claimed. The advantages are said 
to be shorter washing time, less swelling and retention of water, with consequent im- 
provement in the jelly strength of the wet emulsion, and reduced drying time. In 
the present investigation the conditions as to pH of the solutions, and wash-water, 
rate of flow of water, residual thiosulfate, etc., were controlled accurately. The re- 
sults indicate that with a regular acid fixing and hardening bath ( F-25) there is no 
advantage, but rather a disadvantage in washing at the isoelectric point (ca. pH 4.9} 
rather than at pH 7 to 8, since the time required to remove hypo to the same degree is 
increased, nor is less water retained. In a non-hardening acid fixing bath, there was 
little difference in washing time, but some gain in drying time for the isoelectric wash 
because of reduced water absorption. 

The principal object of washing processed film is to remove as 
completely as possible the salts of the fixing bath, and particularly 
thiosulfate, otherwise "hypo." The retention of relatively very 
small amounts of hypo makes the image liable to discoloration and 
deterioration. 1 The investigations of Hickman and Spencer 2 have 
demonstrated that with efficient mechanical conditions hypo can be 
washed out of a photographic (plate) layer of normal thickness in 
quite a short time; they estimated the permissible residue in terms 
of the lowest density it was desired to conserve (against sulfiding or 
sulfating) then assuming a safety factor of 10, suggested 0.00016 
gram per sq. decimeter, or about 0.008 mg. per sq. inch. However, 
in their investigations no particular attention was paid to H con- 
ditions as effecting the efficiency of washing. 

Recently this factor has been considered by D. K. Allison, 3 who 
claims that washing should be done with water adjusted to the 
isoelectric point of the gelatin used in the emulsion. He states that 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 21, 1938. Communication No. 666 from the Kodak Research Laboratories. 
** Eastman Kodak Company, Rochester, N. Y. 


68 S. E. SHEPPARD AND R. C. HOUCK [j. s. M. P. E. 

washing is accomplished in shorter time with consequent smaller 
water absorption by the gelatin, hence also less water consumption 
and shorter drying time. In his U. S. Patent 1,954,512 (1934) he 
proposes to have the pH of both fixing bath and wash water adjusted 
to the same value. In discussion of this proposal 3 it is stated that 
"At pH values other than the narrow range of maximum efficiency, 
the salts such as hypo and alum are chemically combined with the 
gelatin and can not be entirely removed." (Italics in original.) This 
statement is not precisely correct. In general, gelatin as an am- 
photeric electrolyte does not combine with salts, but with ions; at 
pH values lower than the isoelectric point, the gelatin becomes more 
negatively charged and has a greater attraction (electrostatic) for 
anions, while the converse is the case for pH values greater than the 
isoelectric point, when the attraction for anions diminishes, but in- 
creases for cations. These facts are currently employed in processes 
of de-ashing gelatin, 4 the removal of anions (SO 4 , PO 4 , Cl, etc.) being 
effected by washing with alkaline water pH. 810, then the com- 
bined cations are removed by washing in weak acid (dilute acetic, 
pH ca. 4), finally with distilled water, pH 5.5, which removes excess 
acetic until the pH approaches the isoelectric point, ca. pH 5. The 
isoelectric point of gelatins used in photographic emulsions may vary 
from about pH 4.7 to pH 5.2. As the pH of wash water is lowered 
from about 7.5 or 8 (service water) to 5 or lower, the attraction for 
SzOz (thiosulfate) and SO 3 (sulfite) ions is increased, and their re- 
moval is not facilitated, but hindered. In the paper and patent of 
D. K. Allison, no criterion is given of completeness of washing in 
respect of removal of hypo, nor is the washing procedure described 
in any precise fashion. In view of the facts and claims cited it 
seems desirable to study the effect of pH upon washing, using a 
mechanically reproducible procedure, and an efficient test for re- 
moval of hypo. 


All the experiments were made at 18C (64.4F). The emul- 
sion used was Eastman motion picture positive. The solutions used 
during processing are outlined below : 

(1) The developer was D-16 without the developing agent. The 
developing agent was omitted to facilitate the test used to determine 
satisfactory washing. This will be described separately. The time 
of development in all cases was 5 minutes. 

July, 1938] 



(2) A rinse water of 15 seconds was inserted between the de- 
veloper and fixing bath. This rinse water was the same as the final 
wash water. 

(3) Various fixing baths were used. The first tests were made 
with F-25, an acid hardening fixing bath recommended for use with 
Eastman motion picture positive film. The pH was varied from 4.1 
as received to pH 4.8, depending upon the test. 

Other experiments were made with non-hardening fixing baths. 
The pH was varied in these cases from pH 4.1 to 4.8. The time of 
fixation in all cases was 5 minutes. The results with hardening and 
non-hardening fixing baths will be described separately. 

(4) The wash water used was tap water with a pH, as taken, 






FIG. 1. Diagram of washing apparatus. 

varying from 7.8 to 8.0. In part of the experiments the pH of the 
tap water was reduced to pH 4.8 by addition of acetic acid. 

The rate of flow of water through the washing apparatus was 275 
cc. of water per minute. This was checked during each experiment. 

The film to be washed was wound onto a reel from an adjustable 
Kodak film tank. This reel gives a continuous Vs-inch separation 
of the film throughout its entire length of 5 feet. The reel fits nicely 
into 1500-cc. beakers, which were used in the processing. After 
developing, rinsing, and fixing, the reel was connected to the shaft of 
a Cenco Motsinger vacuum stirrer and lowered into the washing 
vessel. This stirrer is operated either by water suction or vacuum 
pump, and gives an up-and-down movement of 69 times per minute. 
The wash water was siphoned from the container in the thermostat 
at the rate of 275 cc. per minute. The washing set-up is shown 
diagrammatically by Fig. 1. 


S. E, SHEPPARD AND R. C. HOUCK [j. s. M. P. E. 




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S. E. SHEPPARD AND R. C. HOUCK [J. s. M. p. E. 

Washing was continued until a negative azide test on the fixed 
emulsion itself was obtained. The azide test used was that de- 
scribed by Jelley and Clark. 5 The solutions were made as described 
and recommended by them. The test was made on the gelatin 
surface instead of the wash water. A definite amount of the test 
solution 0.05 c. c. was placed upon the gelatin surface after removing ex- 
wash water by blotting. This solution was spread over a square- 
inch of surface. If the blue color persisted after one minute, the film 
was considered washed. The time in minutes to reach this point 
was taken as the washing^time, tests being made every two minutes. 
The test was facilitated by using D-16 without developing agent, 
the change from blue to colorless being easy to see. 

Percentage gains in weight, drying rates, and drying times were 
determined on the washed film. The drying rate and drying time 
were determined by removing the excess water from the washed film 
by blotting off with filter paper,, then placing this film in a drying 
atmosphere. The drying was done at 75F with air at 47 per cent 
relative humidity moving over the film at the rate of 60 feet per 
minute. Weighings were made every two minutes until approxi- 
mately constant weight was obtained. The time for the emulsion 
to be dry to the touch was also determined. This is given as the 
drying time in all the tables of data. Actually the emulsion con- 
tinued to lose weight for several minutes after the "dry-to-the- 
touch" point was obtained. The emulsion then was dried further 
over phosphorous pentoxide. The weight of the sample was deter- 
mined by washing off the dried gelatin and weighing the base. From 
the data obtained, the percentage gain in weight was calculated. 

The results obtained with hardening and non-hardening fixing 
baths will be described separately. 

Acid Hardening Fixing Baths. Typical results obtained using the 
acid hardening fixing bath, F-25, at />H 4. 1 are given in Table I. The 
drying curves are given in Fig. 2. 


Effect of pH of Wash Water on the Washing and Drying of Motion Picture Film 
Processed with Acid Hardening Fixing Bath at pH 4.1 

Fixing Fixing 
Bath Bath 




Time to 
"Dry to 

% Gain 

F-25 4.1 
F-25 4.1 

Tap water 
Tap water + 



13-15 min. 
>45 min. 

18 min. 
18-19 min. 


July, 1938] 



As can be seen from the data and curves, lowering the pH of the 
wash water from pH 7.8 to 4.75 has not resulted in a shorter washing 
time but, on the contrary, has increased the washing time consider- 
ably. The drying times are about the same, a fact that one would 
expect since the percentage gains in weight are practically the same. 
Agreement in the drying times is further checked by the drying 
curves. These coincide almost exactly. 


Effect of pH of Wash Water on the Washing and Drying of Motion Picture Film 
Processed with Acid Hardening Fixing Bath at pH 4.74 



Wash Wash 
Water Water 


Time to 
"Dry to 

% Gain 




Tap water 7 . 8 
Tap water + AcOH 4.74 

10-11 min. 
25-26 min. 

18 min. 
16 min. 


Data obtained similarly, but with the />H of the fixing bath in- 
creased to pH. 4.74, are given in Table II and Fig. 3. Again, lower- 
ing the pH of the wash water from pH 7.8 to 4.74 has not decreased 
but has increased the washing time. 

Comparing the case claimed by Allison as giving the greatest gain, 
that in which the fixing bath and the wash water are at the H of the 
isoelectric point of the gelatin, with the one in which the fixing bath 
is at pH 4.1 and the wash water at />H 7.8, it is seen from data in 
Table III that again the time to wash is increased at pYL 4.74, with an 
insignificant gain in drying This is shown in Fig. 4. 


Comparison of Film Processed Normally and Film Processed with All Solutions 
except Developer at pH of Isoelectric Point of Gelatin 

T o y r 


Fixing Fixing 
Bath Bath 

Wash Wash 
Water Water 


Time to 
"Dry to 

% Gain 


F-15 4.1 
F-25 4.74 

Tap water 7 . 8 
Tap water 
+ AcOH 4.74 

13-15 min. 
25-26 min. 

18 min. 
16 min. 



In the case of an acid hardening and fixing bath, when the criterion 
of hypo removal was the azide test, isoelectric washing increased the 
time required for washing, and showed no appreciable gain in drying. 
The azide test, in the presence of gelatin, detects definitely between 
0.05 to 0.01 mg. per sq. inch, which tends to the same order as the 
safety factor suggested by Hickman and Spencer. 



Non-Hardening Fixing Baths. Similar studies were made with 
non-hardening fixing baths, the fixing bath used being F-25 without 
hardening agent. In this case the pR of the fixing bath was raised 
to H 4.72 in all the experiments. 

Typical results obtained are given in Table IV and Fig. 5. 


Effect of pH of Wash Water on the Washing and Drying of Motion Picture Film 
Processed with Non-Hardening Fixing Bath F-22 without Alum 






to Dry 

% Gain 


Tap water 


13 min. 

29-30 min. 



Tap water + AcOH 


13-15 min. 

20-21 min. 





17-19 min. 

23 min. 





21-24 min. 

28-29 min. 


As seen from the data in the table, there is no shortening of the 
washing time on lowering the pH of the wash water from 7.8 to pH 
4.69. Less water is taken up by the gelatin, and this accounts for 
the shorter and faster drying. This decreased drying time checks 
the results obtained by Allison but, on the other hand, the time to 
wash is not materially reduced. If the pH is decreased to pH 4.41, 
the time to wash, per cent gain in weight, and drying time increase. 

It is concluded from the results obtained that washing of an emul- 
sion that has been processed with non-hardening fixing baths is im- 
proved by the use of wash water at the isoelectric point of gelatin 
only in that the amount of wash water taken up is decreased. This 
results in a decreased drying time. 

Our thanks are due to Mr. C. Dittmar, who carried through a 
large number of the experiments described in this paper. 


1 Cf. LUMIERE, A., LUMIERE, L., AND SsYEWETZ, A.: "The Fading of Positive 
Photographic Prints Printed on Chlorocitrate of Silver Paper, Toned and Fixed 
in One Operation," Phot. J., 42 (Nov., 1902), No. 10, p. 225. 

2 HICKMAN, K. C. D., AND SPENCER, D. A.: "The Washing of Photographic 
Products," Phot. J., 62 (May, 1922), p. 225. 

3 ALLISON, D. K.: "Accurate Lab. Control. Pt. 3. H in Processing," In- 
ternal. Phot., 9 (June, 1937), No. 5, p. 35. 

4 NORTHROP, J. H., AND KUNITZ, M.: "Preparation of Electrolyte-Free 
Gelatin," /. Gen. Physiol., 11 (May 20, 1928), No. 5, p. 477. 

8 JELLEY, E. E., AND CLARK, W.: "A Sensitive Test for Thiosulfates," Phot. 
J., 70 (May, 1930), p. 234. 



Summary. Attempts to record on 16-mm. color-film the structural changes taking 
place during the 21-day incubation period of the hen's egg present problems varying 
with each day's growth. Because the authors were working with living subjects that 
required strict adherence to narrow tolerances in order to maintain normal embryo- 
logical development and even life itself, it was necessary to adapt photography to the 
problem not the reverse, as is often possible. 

Development of the embryo is shown in three different ways, i. e., by transmitted 
light, with shell entire; removal of part of the shell and subsequent photography by 
reflected light; removing the entire shell and placing the embryo in a watch crystal, 
thus showing all parts in relative sizes. 

In all three methods, temperature, humidity, and light control constituted the major 
problems. Special equipment devised to meet the requirements of both normal incuba- 
tion and photography had to be built, and the use of mineral oil to obtain a transparent 
plane surface over the opaque, irregular., inner membrane of the egg's air-cell was 

Color motion pictures have provided a distinct contribution in reproducing accu- 
rately the structural changes occurring during the incubation period. 

The recent introduction of easily manipulated color-film has now 
made possible the recording of biological phenomena that hitherto 
have been unsuccessfully reproduced on black-and-white film. This 
results because of the distinct limitations of black-and-white film in 
recording brightness differences that become immediately obvious 
when portrayed in color. 

A biological occurrence of this kind has recently been solved by 
Professor Alexis Romanoff, of the Poultry Department of Cornell Uni- 
versity, and the author. The problem was to show the process of 
development that takes place during the 21 -day incubation period of 
a hen's egg. Inasmuch as the authors were dealing with problems so 
close to the creation of life, namely, the formation of a living animal 
as it progresses through the delicate changes preceding hatching, and 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 19, 1938. 

** Cornell University, Ithaca, N. Y. 


76 E. S. PHILLIPS [J. s. M. p. E. 

final independence as an individual, photographic methods had to 
be limited to the narrow tolerances vital to maintaining normal 
development and even life itself. 

The Motion Picture, Very few persons have witnessed the miracu- 
lous transformations that take place within the protective shell of an 
egg as a new living creature develops. In the short period of three 
weeks a seemingly inert object assumes definite form, emerges from 
its confining walls, and independent life begins. To portray this 
miracle adequately, the authors and Mr. Meade Summers of the 
Ralston Purina Company, sponsors of the project, determined to 
show development in three ways. The first series of pictures depicts 
growth as seen through the shell wall by means of transmitted light. 
The second series was made by cutting a hole about one inch in di- 
ameter at the blunt end of the egg. With the proper lighting align- 
ment it was possible to see clearly within the egg itself. In the third 
series the entire contents of the shell were emptied into a large watch- 
crystal. As a grand finale an egg actually hatches before the camera 

Problems Involved. The problems involved in filming this sequence 
of events were the same as those in controlling normal incubation con- 
ditions. The temperature of the egg had to be maintained at 99 l /2 F. 
Humidity, although not so critical as temperature control, never- 
theless had to be kept as near the optimum value as possible. Since 
normal development was shown three different ways, these conditions 
varied slightly in each case. 

Photographic Equipment. The photographic equipment consti- 
tuded a 16-mm. Eastman Special camera with a 1-inch //1. 9 lens, a 
3-inch //4.5 lens, and a 4-inch f/2. 7 lens. The time-lapse mechanism 
made expressly for the Eastman Special was used for all pictures taken 
by transmitted light. 

Pictures by Transmitted Light. Commercial hatcherymen normally 
view incubating eggs by candling; that is, by placing the unbroken 
egg before a light-source and viewing the contents by transmitted 
light. To duplicate this practice a special incubator box and lamp- 
housing were designed, shown in Fig. 1 . Light from a No. 4 photo flood 
lamp passed through a water-cell which removed heat radiating from 
the bulb. Slightly above the water-cell a condensing lens focused 
the light upon the egg. The egg was supported by an opaque, velvet- 
covered mat with a hole the exact shape but slightly smaller than the 
minimum egg size. The entire mat was held in a glass- covered incuba- 

July, 1938] 



tor box. A velvet-lined tube extended from the plate-glass covering 
of the incubator box to the camera lens, to protect the egg from any 
possible extraneous light. Heat within the box was supplied by 
ordinary resistance wire, controlled by a thermostat to within 0.2 F. 
To guard against short periods of overheating, a water cooling-coil 
was installed. Conduction of heat from the lamp-housing was re- 
duced by forced ventilation. The same incubator box was used with 

FIG. 1. Incubator box and lamp house. 

but slight modification for all the pictures portraying embryonic de- 
velopment by other methods. 

The f/2.7 4-inch lens was used in making all pictures by trans- 
mitted light. Exposures varied on Type A Kodachrome film from l / 30 
second per frame for a fresh egg to 6 seconds per frame for the 20-day- 
old embryo. This wide range was caused by the increasing opacity 
of the growing embryo. 

Embryo Viewed through Aperture in Egg-Shell. The second series 
in the motion picture shows the development of the embryo as seen 
from the blunt end of the egg. Preparing specimens for this series 
was extremely difficult, particularly from the 5th to the 13th day of 



[J. S. M. p. E. 

Mineral Oil 




incubation. Professor Romanoff skillfully removed both the shell 
and the shell-membranes at the large end of the egg. When that was 
done it was possible to look within the shell and clearly see the de- 
veloping embryo. This procedure was followed until the embryo was 
13 days old, at which time removal of the inner membrane became so 
difficult (because hemorrhages were invariably produced) that a new 
method had to be employed. In its normal state this membrane is 
white and practically opaque. After considerable experimentation 
the authors evolved a technic old in principle but new, it is believed, 
in application. When painted with an oily substance the membrane 
became transparent. But to complicate the photographic problem 

the membrane wrinkled and pro- 
duced innumerable highlights 
which precluded any possibility 
of a clear-cut picture. Any 
movement on the part of the 
embryo changed the surface 
structure and accentuated the 
undesirable effect. Mineral oil 
floated upon the invaginated 
inner shell membrane (at the 
air-cell space) provided the most 
satisfactory solution (Fig. 2). 
In addition to making the mem- 
brane transparent the oil formed 
a plane surface through which it 
was possible to photograph clearly. By building the oil surface con- 
siderably higher than the membrane, embryonic movement pro- 
ceeded without inducing any photographic difficulties. 

In Fig. 3 is shown the incubator box, with the egg placed vertically 
on a black-velvet-covered base. This support was made slightly 
smaller than the sides of the box to allow free air circulation. The 
cover was plate glass. Two lights with reflectors were placed approxi- 
mately 32 inches apart; one, a No. 2 photoflood, was 17 inches from 
the egg; and the other, a No. 1 photoflood, was 15 inches from the 
egg. The two lights and the egg were aligned on the same axis at a 
30-degree angle to the glass top. This eliminated direct reflection 
from the oil surface, cast enough shadow to emphasize delicate struc- 
tural details, and gave an illusion of depth. 

The greatest difficulty encountered in filming these activities was 

FIG. 2. Mineral oil placed upon the 
inner membrane to produce trans- 

July, 1938] 



to maintain strict temperature control. If the temperature became 
too high, embryonic movement was accelerated, and the converse was 
true with temperatures lower than normal. The reason is obvious 
when we consider the high radiant energy emitted from the two light- 
sources. Although it is true that this entire series of pictures was 
made without controlling radiant energy, if the work were to be 
duplicated, either water-cells or heat-absorbing glass would be used. 
Determining the exact exposure was exceedingly difficult because 
the reflectivity of the embryo changed from day to day as it under- 
went structural changes. In general, it may be said that the first few 
days of development required less exposure than the intermediate 
stages, and the last few days of growth the least exposure because of 




- c 

- i ) 



- EMtlBM 


FIG. 3. 

Incubator box, with egg placed vertically on velvet- 
covered base. 

the formation of down and its high reflecting value. The lens used 
for these pictures was the 4-inch //2. 7, and the exposure was approxi- 
mately 1 / 80 second at f/8. 

"Close-ups" of the heart presented an interesting problem in focus- 
ing. Since the working distance between the lens and the subject 
was very short, focusing had to be very critical. However, it is well 
known that when an egg's contents are placed upon an approximately 
flat surface sagging of the yolk occurs. Thus, it is obvious that as the 
yolk slowly receded, the embryo, which was on the top surface of the 
yolk, moved away from the lens, thus throwing the picture out of 

Pictures with Embryo in Watch- Crystal. The third series, showing 
the egg's contents emptied into a watch-crystal, presented approxi- 
mately the same difficulties as did the preceding pictures, with two 
exceptions humidity and radiant energy. With much of the egg 

80 E. S. PHILLIPS [J. s. M. P. E. 

content exposed to the air, both evaporation and absorption of radiant 
heat were increased, thus accentuating the effects noted in the pre- 
vious series. 

Hatching Pictures. The most tedious series of exposures were 
those made at the hatching period. Relative humidity had to be 
maintained at 65-70 per cent to insure a normal hatch. Because 
of the high humidity, condensation upon the glass cover of the incu- 
bator box made photography difficult. Also, the emerging chick 
was extremely conscious of visible light and often ceased all activity 
as the exposure was made. However, the greatest difficulty arose 
because of extreme variations in the hatching time for each individual, 
for some chicks emerged in ten minutes and some in three hours. 

General. So far as general comments are concerned the motion pic- 
ture Where Chick Life Begins took three months to produce, more 
than 2000 eggs were used, and five separate originals were made at 
the same time. It should also be said that, with the exception of cer- 
tain scenes incorrectly exposed, the fidelity of color reproduction is 
excellent. At the present writing more than 40,000 persons in all sec- 
tions of this country and parts of Canada have seen the picture, and 
more than 500 written requests (from all over the nation) for its use 
have been refused. 

It is this author's opinion that if we exclude the interest inherent 
in the subject itself, the enthusiastic reception that this picture has 
received is due more to its reproduction in color than to any other 
technic involved. Furthermore, if the picture may be regarded as a 
fair example of what can be done in the biological sciences, the latent 
possibilities for similar projects are enormous in variety and number. 


MR. KELLOGG: How much film footage was used? 

MR. PHILLIPS: That is difficult to say, because in addition to the three months 
for making the picture, there was about a month of experimental work, during 
which we used probably 400 or 500 feet of film to determine the exposure ex- 
perimentally. We often had pictures that did not show what we wanted to show, 
from an embryological point of view, so we had to discard them. So far as 
exposure is concerned, we lost about 500 or 600 feet and used approximately, as 
a grand total, about 8000 feet of film. 

The film has been shown in a great many schools throughout the country. The 
Purina Company received four copies and the University one, and Professor 
Romanoff has shown the film extensively in schools of higher education. 

MR. ROGER: I wish to congratulate the makers of this film, Professor Romanoff 
and Mr. Phillips, for the excellent material we have had the opportunity of seeing. 


I have produced a lot of such material myself, not only on embryos but also on 
living tissue and blood cells, and I realize how difficult it was to get the material 
together and make the picture. As Mr. Phillips has indicated, temperature and 
conditions of light, heat, and so on have much to do with the success of the film. 

MR. TUTTLE: What was the relative humidity during the incubation period; 
and how long do the embryos live? 

MR. PHILLIPS: The relative humidity was approximately 70 per cent, slightly 
above the value for normal incubation. 

The eggs with the shell opened at one end may be capable of hatching, but in 
our work we used mineral oil at the opening, which caused suffocation of the 
embryo in a relatively short period of time. The embryos broken into the 
watch crystal did not live more than a few minutes, or at the most several hours. 

MR. KELLY: The chick's supply of oxygen depends upon a continuous supply 
through the shell, does it not? 

MR. PHILLIPS: Yes. The shell is permeable, as is also the membrane. This 
allows for interchange of gases. 

MR. KELLOGG : How do you dispose of waste products, or render them harm- 

MR. PHILLIPS: Aside from carbon dioxide, the waste is not a large item; it is 
usually left in the alantoic sac, as it is called, at hatching. 



Summary. The success of two U. S. documentary films, "The Plow That 
Broke the Plains" and "The River," written and directed by Pare Lorentz, has focused 
new attention upon this type of film. The school of Public Affairs of American 
University conducts a film course of eight weeks, with screenings, film analyses, and 
discussions conducted by visiting experts in film-making and film use. The subjects 
covered are: the newsreel as contemporary historian; the "March of Time" as a docu- 
ment; federal, educational, and scientific films; U. S. Government documentary 
films; documentary aspects of Hollywood films; foreign documentaries; industrial, 
sales, and domestic propaganda films. Technical aspects with reference to advances 
in film production were discussed. 

In addition to regular discussion and study, a number of reports were made on docu- 
mentary film activities. Among the most important was a complete survey of all U. S. 
government films. 

The emergence of the documentary film as a medium of social 
expression is a significant development in the evolution of the modern 
motion picture. Without seeking a definition of this new film form, 
producers have gone forward and made films of extraordinary social 
value. The documentary form has developed with amazing speed 
and success. While film experts indulge in "streamlined" scholasti- 
cism trying to define the word "documentary," films have evolved in 
many parts of the world that transcend the temporary values of the 
entertainment film, and are making their own definition of the term. 

This new form has had a surprising growth abroad both on the 
Continent and in Great Britain. Its most representative exponent 
in this country is Pare Lorentz, who made The Plow That Broke the 
Plains and The River for the United States Government. The atten- 
tion attracted to the new form, particularly to the Lorentz films, has 
given impetus to the study and production of the documentary form. 

Definitions of varying refinement, charges, and countercharges 

* Presented at the Spring, 1938, Meeting at Washington, D. C. ; received 
April 15, 1938. 

** School of Public Affairs, American University, Washington, D. C. 



hurled at the documentary film have stimulated the curiosity of those 
working with human equations, especially those engaged directly or 
indirectly in educational or public relations work. 

The course, "Documentary Films Today," was instituted at Ameri- 
can University, School of Public Affairs, to round out a constantly 
expanding curriculum encompassing the various- technics used in 
public relations. The School of Public Affairs' "in-service" training 
school for government employees is taught by recognized experts 
in the government. It was for this group that the course was inaugu- 

"Documentary Films Today" was offered for the purpose of giving 
some direction and guidance along the lines of contemporary docu- 
mentary production. It was not offered as a technical or production 
course, but rather as a survey course that would include discussions of 
technical changes in motion picture production. 

Given for a period of eight weeks, the study necessarily had to be 
both intensive and flexible. In order to dissipate some of the con- 
fusion created by pat definitions of the documentary film by the 
critics, the students were shown films recognized as documentary or 
as having documentary aspects. Nearly sixty reels, including 
twenty-one different subjects, were screened, while five guest speakers, 
acknowledged experts in their field, supplemented the lecture mate- 
rial. By going to the material contained in various documentary 
films, it was felt that a truer definition of the new film form could be 
gained. The general scheme of the course ran along the following 
lines : 

The rise and growth of the documentary film. 

The newsreel as contemporary historian. 

The March of Time as a document. 

Federal, educational, scientific, documentary, and action program films. 

Documentary aspects of the Hollywood film. 

Foreign documentary films. 

Industrial, sales, and propaganda films. 

The film for the future historian. 

The opening lecture pointed out by specific example the general 
distinctions between a Hollywood story film, the regular educational 
or scientific film, and the documentary film. The general survey was 
followed by a showing of governmental, educational, scientific, and 
action program films. 

Mr. Fanning Hearon, Director of Motion Pictures of the Depart- 
ment of the Interior, spoke to the class before the showing. He out- 

84 A. A. MERCEY [j. s. M. P. E. 

lined various methods of making government films; and following his 
lecture, conducted the class through the film laboratories of the De- 
partment of the Interior. Hands by the WPA, and In the Beginning by 
the U. S. Department of Agriculture were outstanding subjects on 
this program. Other films included those from the Department of 
the Interior, The Social Security Board, The Federal Housing Ad- 
ministration, and the U. S. Army. 

Both The Plow That Broke the Plains and The River were screened 
after a lecture explaining problems of production, administration, and 
distribution. A general outline under the general title, "From Script 
to Screen," answered questions previously raised by members of the 

The Adventures of Chico, produced by Stacy and Horace Woodard, 
was given a pre-release screening for the class in the discussion of 
documentary aspects of the entertainment film. 

Two outstanding modern films were included in the section devoted 
to foreign documentaries : Housing Problems, a British film, by Arthur 
Elton and Edgar Anspey, and Triumph of the Will, a German film 
of the Nazi festival at Nuremburg, filmed by Leni Riefenstahl. 

The Birth of a Nation, D. W. Griffith's classic, and Sergi Eisen- 
stein's Potemkin illustrated the documentary aspects of the historical 

A program of industrial and propaganda films gave the class a 
general idea of the progress being made in these fields. Progress on 
Parade and Where Mileage Begins, both General Motors' pictures and 
Voices in the Air and Getting Together, Bell Telephone productions, 
were screened. 

H. S. Fitz, assistant in customer relations of the Chesapeake & 
Potomac Telephone company, gave the point of view of the industrial- 
ist who uses films for winning public favor. Floyd Brooker, now as- 
sociated with the film project of the American Council on Education, 
and an accomplished script writer, presented the problems of the 
educator in regard to new industrial and propaganda films. 

The American Way, sponsored by the National Defenders, and 
Death to the Open Shop, made by the United Automobile Workers of 
the CIO, illustrated a sharp contrast in objectives in the propaganda 

J. G. Bradley, Chief of the Division of Motion Pictures and Sound 
Recordings of the National Archives, described to the class the most 


modern methods yet devised to preserve films for the future historian. 
He escorted the class through the motion picture division and ex- 
plained the facilities for screening, classifying, and preserving films 
for tjie Archives. The students also heard Pare Lorentz speak at a 
Washington forum on the difficulties affecting production of the docu- 
mentary film. 

Since the time of the course was so limited, many important phases 
of film making of direct and indirect value to documentaries had neces- 
sarily to be omitted. Supplemental material given the students, 
however, included: preliminary and extensive bibliography of film 
writings; glossary of film terms; condensation of lecture notes; 
folders, lithographs, and scripts of The Plow and The River; program 
notes on the industrial, foreign documentary, propaganda, and histori- 
cal films; and lists of outstanding newsreels and best films of the 

A word about the personnel of the class might be of interest. 
The course included one person who had written a dozen books, one 
who was formerly instructor of English at the University of Wisconsin, 
a chief of exhibits of one bureau, a film chief of another, the wife of a 
high bureau official, and editors and publicity experts from other 
bureaus. The class was of rather exceptional caliber. 

Reports were prepared by the students in lieu of the examinations 
customarily given in the School of Public Affairs. Included in these 
reports was a Federal film survey, the first of its kind ever done. 
This survey includes history, administrative description, and the 
work of various Federal film units. This report has long been needed 
and answers a demand by educators and industry for authentic and 
complete data on the Government's motion picture activity. It is 
now being edited for final presentation in a form to be announced 

The course proved unequivocally that a definite need exists for 
film courses of this kind, which give direction and guidance to stu- 
dents, especially those of adult-education groups, who are working 
with publicity, educational, or training groups. 

The Society of Motion Picture Engineers might well perform a ser- 
vice to the schools by articulating a course giving a definite approach 
to film study. The need exists for such a course, and the Society 
would make a real contribution to contemporary thought, if it ful- 
filled such a mission. 

86 A. A. MERCEY 


MR. WOLF: Did you limit your work to documentary and propaganda film? 

MR. MERCEY: Since the course was only eight weeks long we could take up 
very little else. We did give some attention to documentary aspects of entertain- 
ment films, but there has been so much confused discussion about documentary 
films that we tried to give what we could to eliminate some of the haze. The 
course was a part of a series of courses in public relations, so we had to gear the 
film course to its influence upon public relations, not educational primarily, not 
entertainment, but the course for which it was designed. 

MR. WOLF: Do The Plow and The River represent all the government pictures? 

MR. MERCEY: No. I mentioned those two because it happened that I was 
identified with the production and distribution of them. I would advise those 
who are interested to obtain a complete list from the National Emergency Council, 
which has a complete list of film units and film sources. Many of the films listed 
are documentary; some are educational, some are scientific. 

MR. WOLF: Are all these films produced in the government departments 
photography, laboratory and studio work, and so forth? 

MR. MERCEY: No, the Department of Agriculture and the Department of the 
Interior both produce films in their own laboratories from the time the script is 
written until the film is shown. The films we made were not so produced. We 
hired cameramen on a per diem basis and worked in commercial studios. Our 
work was done in New York commercial laboratories, and some work in Holly- 
wood. There are three ways of making government films : One is through govern- 
ment laboratories such as the Interior and Agriculture Departments have; another 
by engaging per diem employees, and the third, through the contract method, 
which has been used by the Social Security and Federal Housing and other 


During the Conventions of the Society, symposiums on new motion picture appara- 
tus are held, in which various manufacturers of equipment describe and demonstrate 
their new products and developments. Some of this equipment is described in the 
following pages; the remainder will be published in subsequent issues of the Journal. 



A very compact and light-weight variable-width recording optical system has 
been designed for newsreel cameras. Fig. 1 shows the system as it appears 
mounted upon a camera and ready for use. It is 6 inches long, 4 inches wide and 
3 7 /g inches high, and weighs about 3 l /4 pounds complete and ready to record. 
The mounted system shown in the figure extends about 5 inches back from the 
supporting camera wall. Advanced performance and new design features char- 
acterize the system, as it is really a studio recording system 1 compressed to news- 
reel proportions, embodying the more important recent advances in studio 
recording optical system design. 

Sound negatives made on panchromatic film by this system are freer of distor- 
tion and ground-noise than has hitherto been possible with panchromatic film. 
By exposing the track with ultraviolet light (in the range of 3000 to 4300 A) 
irradiation within the emulsion and attendant spread of the developed image are 
reduced. An improvement is thus obtained in frequency response and wave- 
form, similar to that resulting from recording with ultraviolet light 2 on the special 
sound recording emulsions used in studios. The aperture plate or mask of the 
system is designed to produce the Class B push-pull form of the variable-width 
sound-track. 3 As a result, a very substantial reduction in ground-noise is effected 
without the employment of a ground -noise reduction -amplifier and ground - 
noise shutter equipment. In addition to this "free" ground-noise reduction, the 
push-pull form of the track contributes to improved fidelity by effectively sup- 
pressing the distortion that occurs with amplitude-modulated high frequencies, 
such as sibilants, when the normal spread of the negative image is not com- 
pensated for in printing. Prints from a single negative having a wide range of 
density are equal in fidelity and differ only in respect to surface-noise and overall 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 15, 1938. 

** RCA Manufacturing Co., Camden, N. J. 




FIG. 1. Optical system as it appears on the camera. 

FIG. 2. Enlargements from panchromatic 
negative tracks made with the system: (top] 
overshot ultraviolet Class B push-pull; 
(center) white-light bilateral and ultraviolet 
bilateral, 6000 cps. ; (bottom) normally modu- 
lated ultraviolet Class B push-pull panchro- 

July, 1938 J 



output. This is important in a single-film system where negative development 
is determined by the character of the picture and its exposure and the sound- 
track has to come out as best it can. Fig. 2 shows two speech-waves made by 
the new system with ultraviolet light, and two comparison tracks, at 6000 cps., 
made with ultraviolet light and with white light. The tone tracks were pur- 
posely made in the bilateral form to facilitate comparison and measurement. 
The fully modulated Class B push-pull track has the standard width of 0.076 inch 
with a 0.006 septum separating its two portions to assure against overlapping in 
reproduction. The zero lines connecting the modulation segments are each 
0.001 inch wide. The Class B push-pull prints from ultraviolet panchromatic 
negatives have a ground-noise level 50 db. below 100 per cent modulation, which is 
12 db. below the ground-noise level of a print from a comparable standard track 
ultraviolet negative having no ground -noise reduction. 

The curves of Fig. 3 show the frequency-response of tracks made with the new 
system. The upper curve is for negatives made with ultraviolet light, and the 
lower for those made with white light. Both are printed with ultraviolet 
light. At full lamp current (4.3 amperes) the ultraviolet negative has a density 
between 1.0 and 1.2, depending upon development, and it is recommended that 

1 1 1 







1 PRI 




1301 UV PR 
















' ""B 


















, , 










1000 10000 

FIG. 3. Frequency-response of ultraviolet prints from 
panchromatic ultraviolet and white-light negatives made 
with the system. 

the print density be made equal to the negative density, although that is not 
absolutely essential. When recording with white light, this range of density is 
obtained with a lamp current of about 3 amperes. 

Although the new system is extremely compact, it is complete in all details. 
All the usual adjustments of lamp, galvanometer, focus, track location, etc., are 
provided. Some of these features are shown in Fig. 4. The lamp is mounted in 
a cavity or "lamp house" at one corner of the system and may be adjusted in all 
three planes and firmly locked in its required position. At full current, 21 watts 
of power are dissipated in the lamp. Cooling fins are provided on the main part 
of the casting to aid the escape of the heat. It is found, however, that the large 
mass and surface of the camera to which the system is secured prevent an ap- 
preciable temperature rise from this source even when the lamp is operated for 



considerable periods of time. In practice the lamp is interlocked with the camera 
motor switch and is turned on only while the camera operates. The lamp in- 
stantly comes to full brilliance. The galvanometer can be rotated about its 
vertical axis and locked in the required adjustment by the two opposing screws 
at the back of the system. A thumb-nut, accessible underneath the system and 
protected by a guard, adjusts the galvanometer about its horizontal axis. A 
focus adjustment knob is graduated in thousandths of an inch to permit accurate 
adjustment of the distance from the objective lens to the film, and may be easily 
reset to care for any change in thickness of film stock. (The objective moves 
independently of the slit which is fastened to the main casting.) A lock-screw at 
the side of the system secures this adjustment after it has been made. The 
ultraviolet filter is specially mounted so that it may be turned easily to one side 









FIG. 4. Optical system with covers and galvanometer removed. 

to permit recording with white light, a clear glass plate taking its place to provide 
the required optical compensation. The provision for white-light recording allows 
the demand upon the power supply to be reduced in cases of necessity as the lamp 
then operates at reduced current. The entire system is mounted upon a special 
plate, a groove in the casting cooperating with a tongue on the plate for azimuth 
adjustment. The tongued plate is in turn secured to the camera by screws and 
dowels. Three screws hold the optical system to the plate, by loosening which 
the system may be moved sidewise for adjusting the track location. A vernier 
scale on the system cooperates with another on the tongued plate to aid in making 
lateral adjustments of the system. The azimuth of both the push-pull aperture 

July, 1938] 



plate and the slit are adjusted and dowelled at the factory. A small auxiliary 
mirror permits the galvanometer mirror to be seen when lamp adjustments are 
being made, and an auxiliary lens and mirror system permit a magnified view of 



FIG. 5. Diagram showing correct adjustment of 
aperture plate image on slit (Note: lines shown heavy 
are engraved on slit face). 

the slit face when adjusting the galvanometer and judging modulation. Fig. 5 
shows the appearance of the correctly adjusted Class B push-pull aperture image 
as seen upon the slit face when looking through the peep lens. The lines marked 
50% and 100% enable the operator to judge modulation amplitude and set the 
volume indicator meter on his amplifier accordingly. 


FIG. 6. Schematic diagram of the optics. 

The optical system proper is of the same general design as the variable-width 
studio system 1 but incorporates certain new design features made necessary by 
its small size. The optical arrangement is shown schematically in Fig. 6. A 



new lamp of 4.9 volts, 4.3 amperes rating (21 watts) is used in an S-S bulb. The 
condenser is somewhat faster than those in the studio systems, having a speed of 
about //I, and is of two elements designed for minimum spherical aberration. 
It is made of crystal quartz to insure against transmission loss in the near-ultra- 
violet. The aperture plate is in a dust-proof mounting between the condenser 
and a quartz dust window. The very limited space requirements make it impos- 
sible to image the aperture plate upon the slit by means of a lens mounted axially 
either preceding or following the galvanometer mirror, and this function is per- 
formed by a galvanometer window lens through which the light passes obliquely 
both before and after reflection from the mirror. This lens is of crown glass and 
so shaped and placed with respect to the mirror as to perform its function properly. 
The condenser at the slit is again of crystal quartz and serves to image the galvan- 
ometer mirror upon the objective lens. The objective lens consists of four air- 
spaced elements, corrected chromatically for 3650 and 5460 A, and having an 
equivalent focal length of 7.6 mm. and a speed of //2. The image of the slit that 

FIG. 7. Frequency characteristic of the galvanometer. 

it forms on the film is 0.076 inch long and 0.0005 inch wide. The filter between 
the slit and objective is of Corning 597, Red Purple Ultra glass of 2-mm. thick- 
ness, and very effectively restricts exposure to the region from 3000 to 4300 A. 

The galvanometer 2 incorporates some recent improvements. Nicaloi is used 
for both pole-pieces and armature to prevent corrosion and further reduce dis- 
tortion. The mirror pivot plate has approximately the same coefficient of thermal 
expansion as glass. It is a stainless nickel iron alloy, and is soldered to the ribbon. 
The curve of Fig. 7 shows the frequency-response characteristic of the galvanom- 
eter. The rise in high-frequency response approximately compensates for film 
loss to 5500 cps. The required power input at 100 per cent deflection is about 60 
milliwatts. Each galvanometer is supplied with a matched capacitor that adjusts 
the characteristic to the form. shown. 3 

Negatives made on the system are printed and re-recorded to the bilateral track 
form with noise reduction for theater release. The system can easily be con- 
verted to produce a bilateral track directly simply by exchanging aperture plates. 

Acknowledgment is due the Bausch & Lomb Optical Company for developing 
the short-focus, wide-field objective used on the system, and further acknowledg- 


ment is due R. F. Brady and F. E. Runge for the excellent mechanical design of 
the system. 


1 SACHTLEBEN, L. T.: "Characteristics of the Photophone Light-Modulating 
System," /. Soc. Mot. Pict. Eng., XXV (Aug., 1935), No. 2, p. 175. 

8 DIMMICK, G. L. : "Improved Resolution in Sound Recording and Printing 
by the Use of Ultraviolet Light," /. Soc. Mot. Pict. Eng., XXVII (Aug., 1936), 
No. 2, p. 168. 

8 DIMMICK, G. L.: "The RCA Recording System and Its Adaptation to Vari- 
ous Types of Sound-Track," J. Soc. Mot. Pict. Eng., XXIX (Sept., 1937), No. 3, 
p. 258. 



In order to assure the high quality essential to sound recording and reproducing, 
it is very desirable to avoid overloads, particularly of the recording device. On 
the other hand, the requirement for maintaining a high signal-to-noise ratio in- 
duces operation as near the overload point as possible. With even the most care- 
ful monitoring occasional overloading is unavoidable. The effects of overload 
may be either degradation of quality or actual injury to the recording device. 
Several forms of devices for the prevention of these have been developed. Their 
application to the field of sound recording is, however, fairly recent. 

One type of amplitude Jimiter that is now being extensively used in the radio 
broadcast field 1 prevents excessive amplitudes by automatically changing the loss 
through a network by an amount that is a function of the amplitude of the signal 
envelope. Since the loss of the system can not be changed instantly without 
noticeable distortion, a time delay 'of the order of 10 to 20 milliseconds between 
the occurrence of the peak and the correcting action of the system is used. A 
time delay of approximately 125 to 250 milliseconds is used to restore the system 
to its normal gain so that the changes are gradual rather than abrupt. Since all 
portions of a wave are attenuated to nearly the same extent over a given small 
interval of time, no apparent harmonics are generated to degrade the quality. 
This kind of limiter will subsequently be referred to as a "peak limiter." A de- 
tailed description of such a device is to be found elsewhere in the literature. 2 

A second type of amplitude limiter to be described herein limits peak signal am- 
plitudes to a predetermined value and is without time delay. It has no effect 
upon signals of lesser amplitude than the critical value and generates harmonics of 
odd order when "limiting." This will be called a "peak chopper." 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 29, 1938. 

** Electrical Research Products, Inc., Hollywood, Calif. 



Comparison of Volume-Limiting Methods. Volume limiting has not up to the 
present time played as active a role in motion picture recording as it has in radio 
broadcasting. Motion picture scenes are generally well rehearsed as to volume 
range, and several "takes" are made. If overload occurs on some takes, others 
may usually be made that are satisfactory ; whereas in radio work it is not always 
possible to foresee what volumes will arise; and, once "on the air," no retakes are 
possible. As a result, amplitude limiters have not been used in the majority of 
motion picture recording sequences. However, there are many cases wherein 
unusual and unpredictable volume relationships occur when the use of a limiter 
is definitely valuable. Whether the peak limiter or the peak chopper type of 
equipment is most suitable depends upon the type of material involved and upon 
the limitations of the recording medium. 

In speech and in certain types of music a small percentage of the peaks may 
reach amplitudes 15 to 20 db. higher than the average signal amplitude. With 

many of the recording systems 
used today, and particularly with 
variable-density systems, the aver- 
age recording volume is set ap- 
proximately 10 db. below the 
modulator overload point. It is 
apparent that if a peak limiter 
that acts upon the signal envelope 
is used under these conditions, an 
appreciable reduction of the under- 
lying signal strength will result, 
which occurs when the peak causes 
the gain through the device to 
change. Compression of the signal 
in this manner results in no un- 
pleasant effects provided the com- 
pression does not exceed 3 db. 
.When greater compression is used 

the loss of volume range may in some cases cause a loss of dramatic expression, 
or "punch." Thus, instead of this kind of limiting, which is harmonic-free, it 
may at times be preferable to allow considerable "overload" to obtain the maxi- 
mum volume. Examples of this sort are gunshots, crashes, hurricanes, battles, 
or other scenes featuring excitement and commotion. Here the peak chopper 
proves most suitable, since it prevents damage to equipment and at the same 
time permits the maximum volume of which the modulating device is capable. 
On the other hand, in dialog scenes of an emotional nature the harmonics pro- 
duced by a peak chopper during overload sequences may be objectionable. Here 
the peak limiter, which automatically reduces gain without incurring harmonics, 
proves valuable. 

Amplitude limiters should be used in a manner adapted to the recording 
method employed. With the variable-width system, for example, the harmonics 
generated with signals exceeding the modulator overload point are somewhat 
more severe than is the case with the variable-density method. This is because 

FIG. 1. Peak chopper circuit. 

July, 1938] 



the space limitations of the sound-track effect a sharp cut-off of both positive and 
negative peaks in the variable-width system, whereas in the variable-density 
system the signal is not so sharply cut off at the overload point. There is a con- 
siderable range available on the film, even though non-linear, which is of value 
in reducing the severity of overloads. Owing to this difference, the usual practice 
has been to operate variable-density recorders with a percentage modulation 
from 4 to 6 db. greater than in the case of variable- width recorders. Use of the 
peak limiter with the variable-density system entails the disadvantage that if 
the limiter operates at the overload point of the valve, a small percentage of the 
peaks will cause a compression greater than the permissible 3 db., giving a notice- 
able "pumping" effect and also a loss in the upper volume range. This effect 
may be avoided by reducing the average volume, but owing to background noise 
this is not generally desirable. Another alternative is to adjust the peak limiter 


FIG. 2. Showing effect of peak chopper on signal. 

to operate at a point 2 to 4 db. above the modulator overload. But in this case 
the harmonic-free result is largely lost. Still another alternative is to permit a 
certain amount of overload for the sake of the volume range and guard against 
damaging signals by using a limiter of the peak chopper type set to operate for 
signal amplitudes 4 to 6 db. above modulator overload. However, for variable- 
width recording systems or for radio broadcasting wherein the overload point is 
sharply defined and may not be exceeded appreciably, the peak limiter or variable- 
gain type provides a useful function for certain types of speech or music. 

A Peak Chopper Equipment. A peak chopper that cuts off excessive ampli- 
tudes without time delay is shown schematically in Fig. 1. Its operation is as 
follows: A copper-oxide rectifier, or varistor, of suitable design has its a-c. 
terminals connected across the line and the d-c. terminals connected to a battery 
having the same polarity as the normal output of the rectifier. Current will flow 
from the line through the rectifier only when the peak voltage exceeds the battery 
voltage. During such periods the device acts very much as a short-circuit, so 
that the line voltage is held down to the predetermined value. For signal vol- 



[J. S. M. P. E. 

NI Miundnv xvid indino 
I I I I 

July, 1938] 



tages lower than this value the device has no appreciable effect. Fig. 2 shows the 
manner in which a sine-wave signal is limited, and Fig. 3 shows the relation of 
output amplitude to input amplitude. Here a 10-db. increase in input signal 
above the threshold results in a 2-db. increase in output amplitude. As the 
threshold value is passed odd harmonics are progressively generated. Even har- 
monics are not produced in the device. When a peak chopper of this type is 
used with a modulating device having resonance in the upper audible range, it is 
advisable to employ a low-pass filter following the limiter. This filter should 
have its cut-off frequency just below the resonance frequency of the modulator. 
Third harmonics generated by the limiter and having values in the neighborhood 
of modulator resonance will thus be incapable of causing trouble. 

Fig. 4 shows the third harmonics introduced by the chopper for signals greater 
than the threshold value. These are of somewhat greater magnitude than those 
introduced by the film under corresponding conditions. However, by setting the 
peak chopper to operate at approximately 4 db. above the modulator overload 
point, when working with variable-density recording, the harmonic generation 

FIG. 5. Peak chopper unit. 

is held down practically to that contributed by the film, and at the same time 
protection is afforded to the modulator against further damaging peaks. 

With variable-width recording devices the threshold may be set at or slightly 
above the modulator overload point, since any harmonic generated will be about 
the same whether generated by the limiter or by the system. 

Fig. 5 shows the appearance of a peak chopper of the type described. A low- 
pass filter is incorporated within the unit for the purpose previously mentioned. 
A six-position switch shown on the right side of the instrument connects the de- 
sired threshold voltage, which is indicated by pressing the push-button shown on 
the left of the meter. The meter reads voltage on one scale, and overload point 
in decibels relative to 0.006 watt across 500 ohms on the second scale. As con- 
structed, the threshold may be set so that limiting begins at a value as low as 
-f-6 db. or as high as +18 db. relative to 0.006 watt. During operation the meter 
acts as a milliammeter in the resistor circuit indicating when overload occurs. 
The degree of overloading obtained is a function of the meter reading (except as 
modified by the lag of the movement) and may be determined by reference to 
calibration curves furnished with the unit. 


Prior to the use of this equipment with light-valve systems, considerable in- 
convenience was experienced in ribbon breakage and changes in adjustment. 
After installation of the peak chopper practically no trouble of this kind that may 
be attributed to overloads was experienced. 

This paper has endeavored to show wherein amplitude limiters have a useful 
function in sound recording. Of the two types of limiters discussed, one com- 
presses the envelope for excessive amplitudes without harmonic generation but 
with a time delay; whereas the other type chops off excessive peaks instantane- 
ously, with generation of harmonics. It is felt that the first type is most useful 
for systems wherein a critical overload point may not be exceeded to any appreci- 
able extent and where such volume compression as results will not be objection- 
able. For other conditions the peak chopper is found useful for the protection of 
equipment against damaging overloads. 


1 HOVGAARD, O. M.: "A Volume Limiting Amplifier," Bell Laboratories Record, 
XVI (Jan., 1938) No. 5, p. 179. 

2 DOBA, S.: "Higher Volumes without Overloading," Bell Laboratories Rec- 
ord, XVI (Jan., 1938) No. 5, p. 174. 

3 HOVGAARD, O. M., AND DOBA, S.: "Higher Program Level without Circuit 
Overloading" (Presented before the Institute of Radio Engineers, May, 1937; 
not yet published). 



The editors present for convenient reference a list of articles dealing with subjects 
cognate to motion picture engineering published in a number of selected journals. 
Photostatic copies may be obtained from the Library of Congress, Washington, D. C., 
or from the New York Public Library, New York, N. Y. Micro copies of articles 
in magazines that are available may be obtained from the Bibliofilm Service, Depart- 
ment of Agriculture, Washington, D. C. 

American Cinematographer 

19 (Apr., 1938), No. 4 
Low Key Lighting May Be as Easy in Color as It Is 

in Monochrome (pp. 146-151) W. H. GREENE 

Agfa Issues Its 35-Mm. Supreme in Spools, Press in 

Rolls and Packs (p. 150) 

Color in Broadcasting Studied by New Hollywood Tele- 
vision Group (pp. 160-161). W. L. PRAGER 
Micro Movies Most Efficient Research Tool (pp. 162- 

164). P. A. ZAHL 

European Product Eumig C4 8-Mm. Camera Enters 

American Market (pp. 166-168). 

19 (May, 1938), No. 5 
Arnold Devises Semi-Automatic Follow-Focus Finder 

for Camera (pp. 188-189). W. STULL 

Cine Kodak Secures Added Range in New Eastman 

Focusing Finder (p. 205). 
Bell & Howell Announces 16-Mm. Projector with 

Powerful Arc (pp. 206-207). 
National Archives Will Preserve Motion Pictures for 

Generations (pp. 217-219). J. G. BRADLEY 

Cinematographie Francaise 

20 (Mar. 25, 1938), No.' 1012 

Le Nouveau Super-Equipement Sonore de laKlangfilm- 
Tobis (New Super Sound Equipment of Klangfilm- 
Tobis) (p. IX). 

Spectrometre Electro- Acoustique Siemens (Siemens 
Electroacoustic Spectrometer) (p. X). 


11 (Apr., 1938), No. 4 

Television Receivers, (pp. 29-31, 63-66). E. W. ENGSTROM AND 



100 CURRENT LITERATURE []. s. M. p. E. 

International Photographer 

10 (Apr., 1938), No. 3 

Hollywood's Service Army (pp. 11-13). 

Photography Back on Top New cameras (pp. 15-16, 

Rear Projection Big Advance (pp. 30-33). 

Sound Problems Overcome (pp. 39-42). J. N. A. HAWKINS 

Lighting Pan and Sound Put Inkies on Top (pp. 43- 

Laboratory Science Supersedes Guesswork (Develop- 
ing Machines) (pp. 50-52) D. K. ALLISON 

Light-Sources Big Improvement (pp. 55-58). P. R. CRAMYR 

International Projectionist 

13 (Apr., 1938), No. 4 

The Geneva Intermittent Movement: Its Construc- 
tion and Action (pp. 7-9) (II). A. C. SCHROEDER 

Chaotic Status of Laws Anent Projection Technic, 
Equipment, Rooms Revealed by Nation- Wide 
Survey (Bureau of Labor Statistics, U. S. Dept. of 
Labor) (pp. 15-16) (II). 

Technical Data on New Simplex Sound System (pp. 
17, 26). 

Analyses of Modern Theater Sound Reproducing Units 

(pp. 20-22). A. NADELL 


20 (Apr., 1938), No. 4 
Physiologische Untersuchungen zur Kinoprojektion 

(Physiological Experiments on Motion Picture Pro- H. FRIESER AND 
jection) (pp. 85-92). W. MUNCH 

Die Lichtverteilung hn Filmspaltbild als Quelle nicht- 
linearer Verzerrungen (Light Distribution in Image 
of the Aperture as a Source of Non- Linear Distortion) 
(pp. 93-96) A. NARATH 

Motion Picture Herald (Better Theaters Section) 

131 (Apr. 30, 1938), No. 5 
Perfection of Mercury Vapor Lamp to Bring New 

Lighting Technique (p. 5). 

A New Sound System Designed by a Projection Organi- 
zation (pp. 27-28). 

Photographische Industrie 

36 (Mar. 30, 1938), No. 13 

Die deutsche Photo- und Kino-Fruhjahrsmesse 1938 
(Photographic and Motion Picture Spring Exhibi- 
tion) (pp. 394-406). 

Neue Richtlinien fur Schul-Stehbildwerfer (New 
Standards for School Lantern Slides) (pp. 415-417). 



RCA Review 

2 (Apr., 1938), No. 4 

Equipment and Methods Developed for Broadcast 

Facsimile Service (pp. 379-395). C. J. YOUNG 

The Monoscope (pp. 414-420). C. E. BURNETT 

Some Notes on Video-Amplifier Design (pp. 421-432). A. PREISMAN 

Effect of the Receiving Antenna on Television Recep- 
tion Fidelity (pp. 433-441). S. W. SEELEY 

A 200-Kilowatt Radiotelegraph Transmitter (pp. 442- C. W. HANSELL AND 
458). G L. USSELMAN 




Officers and Committees in Charge 

W. C. KUNZMANN, Convention Vice-P resident 
J. I. CRABTREE, Editorial Vice-President 
G. E. MATTHEWS, Chairman, Papers Committee 
H. GRIFFIN, Chairman, Projection Committee 
E. R. GEIB, Chairman, Membership Committee 
J. HABER, Chairman, Publicity Committee 



Local Arrangements 

K. BRENKERT, Chairman 




Registration and Information 

W. C. KUNZMANN, Chairman 



Hotel and Transportation Committee 

A. J. BRADFORD, Chairman 






H. GRIFFIN, Chairman 






Officers and Members of Detroit Projectionists Local No. 199 




J. F. STRICKLER, Chairman 




J. HABER, Chairman 



Ladies 1 Reception Committee 

MRS. J. F. STRICKLER, Hostess 

assisted by 





The Headquarters of the Convention will be at the Hotel Statler, where excellent 
accommodations' are assured. A reception suite will be provided for the Ladies' 
Committee, who are now engaged in preparing an excellent program of entertain- 
ment for the ladies attending the Convention. 

Special hotel rates guaranteed to SMPE delegates and friends, European plan, 
will be as follows : 

One person, room and bath $3.00 to $6.00 

Two persons, room and bath 5.00 to 8.00 

Two persons (twin beds), room and bath 5.50 to 9.00 

Three persons, room and bath 7.50 to 10.50 

Parlor suite and bath, for one 8.50 to 11.00 

Parlor suite and bath, for two 12.00 to 14.00 

Room reservation cards will be mailed to the membership of the Society in the 
near future, and everyone who plans to attend the Convention should return his 
card to the Hotel promptly in order to be assured of satisfactory accommodations. 
Registrations will be made in the order in which the cards are received. Local 
railroad ticket agents should be consulted as regards train schedules, and rates to 
Detroit and return. 

The following special rates have been arranged for SMPE delegates who motor 
to the Convention, at the National-Detroit Fireproof Garage (the Hotel Statler's 
official garage), Clifford and Elizabeth Streets, Detroit: Self-delivery and pick-up, 
12 hours, $0.60; 24 hours, $1.00; Hotel-delivery and pick-up, 24 hours, $1.25. 
Special weekly rates will be available. 

Technical Sessions 

An attractive and interesting program of technical papers and presentations is 
being assembled by the Papers Committee. All technical sessions, apparatus 
symposiums, and film programs will be held in the Large Banquet Room of the 

Registration and Information 

Registration headquarters will be located at the entrance of the Large Banquet 
Room, where members of the Society and guests are expected to register and re- 
ceive their badges and identification cards for admittance to the sessions and film 


programs. These cards will be honored also at several motion picture theaters 
in the neighborhood of the Hotel, during the days of the Convention. 

Informal Luncheon and Semi- Annual Banquet 

The usual Informal Luncheon will be held at noon of the opening day of the 
Convention, October 31st, in the Michigan Room of the Hotel. On the evening of 
Wednesday, November 2nd, the Semi-Annual Banquet of the Society will be held 
in the Grand Ballroom of the Hotel at 8 P.M. Addresses will be delivered by 
prominent members of the industry, followed by dancing and other entertainment. 

Points of Interest 

In addition to being a great industrial center, Detroit is also well known for the 
beauty of its parkways and buildings, and its many artistic and cultural activities. 
Among the important buildings that one may well visit are the Detroit Institute 
of Arts; the Detroit Historical Society Museum; the Russell A. Alger House, a 
branch of the Detroit Institute of Arts; the Cranbrook Institutions; the Shrine 
of the Little Flower; and the Penobscot Building. 

At Greenfield Village, Dearborn, are grouped hundreds of interesting relics of 
early American life, and there also is located the Edison Institute, established by 
Henry Ford in memory of Thomas A. Edison. 

On the way to Greenfield Village is the Ford Rotunda, a reception hall for visi- 
tors to the Ford Rouge Plant. Here are complete reproductions and displays of 
motorcar design, and representations of the famous highways of the world, from 
Roman days to modern, are on the grounds surrounding the building. 

The General Motors Research Building and Laboratory, located on Milwaukee 
Avenue, will be of particular interest to engineers visiting the City. 

Various trips may be taken from Detroit as a center to Canada, by either the 
Ambassador Bridge or the Fleetway Tunnel; to Bloomfield Hills, a region of 
lakes; Canadian Lake Erie trip from Windsor, Ontario; to Flint, Michigan, 
another center of the automotive industry; to Milford, General Motors' Proving 
Grounds; and to the Thumb of Michigan Resort Beaches. The City contains 
also a number of beautiful parks and golf courses. 



At a recent meeting of the Admissions Committee, at the General Office of 
the Society, the following applicants for membership were admitted to the 
Associate grade: 


Kanai, T. H. 
Altec Service Co., 

2111 Woodward Ave., 

Detroit, Mich. 
210 W. Montcalm St., 

Detroit, Mich. 
GROB, E. F. 

3 Chesterton Flats, 

Manion Ave., 

Rose Bay, 

Sydney, Australia. 

United Detroit Theater Corp., 
1600 Stroh Building, 

Detroit, Mich. 

134 North Hobart Blvd., 

Los Angeles, Calif. 

RCA Photophone (India) Ltd., 
Prospect Chambers, 
Hornby Rd., 

Bombay, India. 

63-01 Alderton St., 

Elmhurst, Long Island, 
New York. 


19303 Pennington Dr., 
Detroit, Mich. 


National Bureau of Educational and 

Social Research, 
Union Buildings, 

Pretoria, South Africa. 


10845 Wellworth Ave., 
West Los Angeles, Calif. 

17 Kambala Rd., 
Bellevue Hill, 

Sydney, Australia. 


SS Manhattan 

U. S. Lines, 1 Broadway, 
New York, N. Y. 


316 M. & M. Bldg., 
Houston, Texas. 


Empire Talkie Distributors, 
Heera House, 
Sandhurst Rd., 
Bombay 4, India. 


California Institute of Technology, 
Pasadena, Calif. 


Empire Talkie Distributors, 
Chandani Chowak, 
Delhi, India. 




Box 68, Balboa Heights, Mariners, Christchurch Rd. 

Canal Zone. Virginia Water, 

STRALEY, W. Surrey, England. 

3725 Warwick Blvd. VAVRINA, E. 

Kansas City, Mo. Prague V, 

TRECELLAS, L. K. Czechoslovakia. 
57 Pollman Court, 
Streatham Hill, 

London S. W. 2., England. 

In addition, the following applicants have been admitted by vote of the Board 
of Governors to the Active grade : 


411 Fifth Ave., 3034 Leland Ave., 

New York, N. Y. Chicago, 111. 


198 Johnson Ave., 34 Hayes St., 

Teaneck, N. J. Binghamton, N. Y. 


1540 Broadway, RCA Manufacturing Co. 

New York, N. Y. Camden, N. J. 


908 S. Wabash Ave., 
Chicago, 111. 




Volume XXXI AUGUST, 1938 Number 2 



Progress in the Motion Picture Industry Report of the Prog- 
ress Committee 109 

The Multiplane Camera Crane for Animation Photography . . . 


Distortion in Sound Reproduction from Phonograph Records 


A Higher-Efficiency Condensing System for Picture Projectors 

F. E. CARLSON 187 

A Color Densitometer for Subtractive Processes. . R. M. EVANS 194 

Report of the Papers Committee ' 202 

Current Literature 212 

Detroit Convention 214 

Society Announcements 217 





Board of Editors 
J. I. CRABTREE, Chairman 



Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscriptions or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 
Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 

West-Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1938, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is 
not responsible for statements made by authors. 


^President: S. K. WOLF, RKO Building, Rockefeller Center, New York, N. Y. 
*Past-President: H. G. TASKER, Universal City, Calif. 
*Executive Vice-President: K. F. MORGAN, 6601 Romaine St., Los Angeles, 


** Engineering Vice-President: L. A. JONES, Kodak Park, Rochester, N. Y. 
^Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 
** Financial Vice-President: E. A. WILLIFORD, 30 E. 42nd St., New York, N. Y. 
* 'Convention Vice-President: W. C. KUNZMANN, Box 6087, Cleveland, Ohio. 
^Secretary: J. FRANK, JR., 90 Gold St., New York, N. Y. 
^Treasurer: L. W. DAVEE, 250 W. 57th St., New York, N. Y. 


*J. O. AALBERG, 157 S. Martel St., Los Angeles, Calif. 

*M. C. BATSEL, Front and Market Sts., Camden, N. J. 

**R. E. FARNHAM, Nela Park, Cleveland, Ohio. 

*G. FRIEDL, JR., 90 Gold St., New York N. Y. 

*A. N. GOLDSMITH, 444 Madison Ave., New York, N. Y. 

**H. GRIFFIN, 90 Gold St., New York, N. Y. 

**A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

*S. A. LUKES. 6145 Glenwood Ave., Chicago, 111. 

*Tenn expires December 31, 1938. 

**Term expires December 31, 1939. 


immary.This report of the Progress Committee covers the year 1937. The 
advances in the cinematographic art are classified as follows: 

(I) Cinematography: (A} Professional and (B) Substandard; (II) Sound Re- 
cording; (III) Sound and Picture Reproduction; (IV) Publications and New 
Books; (Appendix) The Japanese Motion Picture Industry; Progress in Germany; 
Progress in Great Britain. 

The most notable advances recorded during the past year appear 
to have been in the production of new panchromatic emulsions for 
professional cimematography. One emulsion has resulted in addi- 
tional negative speed without any consequent increase of grain size. 
Another new emulsion, intended for newsreel use and work under ad- 
verse lighting, has from three to four times greater speed than stand- 
ard super-sensitive panchromatic films. 

In the field of substandard cinematography the popularization of 
color has advanced rapidly coincidentally with improvement in proc- 
essing of color-films. 

In the field of sound recording there is little to report in the way of 
advances in equipment, the year's activities being largely confined to 
the consolidation of advances previously reported for 1936. 

The modernization of theaters has progressed satisfactorily, es- 
pecially in the matter of installation of the newer two-way horn sys- 
tems announced in last year's report. 

In the projection field there is little to report in the way of new 
equipment, either for sound or picture projection. The Committee 
is including for the first time this year material describing theater 
lighting and marquee illumination. 

The Committee wishes to thank the following companies for supply- 
ing materials and photographs for the report : Ampro Corporation ; 
Bell & Howell Co.; Eastman Kodak Co.; Electrical Research 
Products, Inc.; General Electric Co.; General Service Studios, Inc.; 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 15, 1938. 



General Radio Co.; Mole-Richardson Co.; Paramount Pictures 
Corp.; Victor Animatograph Corp. 

J. G. FRAYNE, Chairman 






(I) Cinematography 
(A} Professional 

(1) Emulsions 

(2) Cameras and accessories 

(3) Stage illumination 

(B) Substandard 

(1) Films 

(2) Cameras 

(3) Projectors 

(4) Miscellaneous 

(II) Sound Recording 

(1) General 

(2) Equipment 

(3) Accessories 

(4) Films 

(III) Sound and Picture Reproduction 

(1) Motion picture theater lighting 

(2) Theater lighting equipment 

(3) Accessories 

(IV) Publications and New Books 
Appendix A 

The Japanese Motion Picture Industry 1937 
Appendix B 

Progress in Germany 
Appendix C 

Progress of the Motion Picture Industry in Great Britain 

(A) Professional 

The year 1937 has seen some very definite progress in the field 
professional motion picture photography. 


(1) Emulsions. Perhaps the outstanding advance for the year 
has been made by the Agfa Ansco Corporation, who developed and 
marketed two new and very fast panchromatic negatives that have 
proved almost revolutionary, in that they have "de-axiomized" the 
old belief that added negative speed always meant increased grain 
size. Conversely, their new negatives, with a very great increase in 
speed, have maintained and even lessened the grain size. The 
Agfa Supreme is a new product having twice the speed of standard 
supersensitive panchromatic emulsions. It retains to the full extent 

FIG. 1. Dual screen transparency camera. 

such essential qualities as keeping stability, color balance, and ex- 
tremely fine grain which, heretofore, were impaired by increased 
speed. It provides the production cameraman with a means of re- 
ducing working camera apertures, with a consequent increase of defi- 
nition and better photographic quality. It minimizes the problem 
of character grouping which, in the past, has been restricted by 
shallow focus. It increases the efficiency, realism, and scope of proc- 
ess projection work, thereby enabling economy to producers. In 
general, it represents a major achievement in research and emulsion 
manufacture by providing the industry with a medium of increased 
latitude and quality. 


The Agfa Ultra-Speed Pan is intended for newsreels and adverse 
light conditions. It has from three to four times greater speed than 
standard supersensitive panchromatic material. It possesses full 
keeping stability and provides the industry with a means of obtaining 
photographic results under adverse conditions heretofore impossible. 
It is of particular value for night scenes photographed under ordi- 
nary artificial illumination and for night scenes of large area with 
special artificial illumination. It increases economy in production 
by permitting work in poor light thereby increasing the working day. 
It provides newsreels with an efficient material under conditions out- 
lined above. 

The Eastman Kodak Company brought out two fine-grain dupli- 
cating films, 1 negative and positive, that are well worthy of note in 
that they bring duplication quality much closer to the original. 
Since speed is not especially essential in duplication, the Eastman 
Company have concentrated upon grain reduction, resulting in an 
extremely fine grain so necessary for ideal results. Duplicate nega- 
tives from lavender positives, using this new fine-grain stock, are 
almost exact replicas of the original, retaining their texture and 
quality. These new stocks have proved highly adaptable to pro- 
jection work, because of their lack of grain and great latitude. 

(2) Cameras and A ccessories. No new cameras have been developed 
during the year, but the Twentieth Century-Fox Camera, described 
last year in the JOURNAL, having successfully photographed eighteen 
productions since its inception, still leads the field. It is of interest to 
note that ten similar cameras are now in course of construction for 
Twentieth Century-Fox, the first to be delivered in April. Since this 
camera will be made available to other studios, its use by the studio 
of origin will be under careful scrutiny during the coming year. 

The semi-automatic follow-focus finder, as used more or less on all 
blimped cameras, has been carried to a high degree of completion at 
MGM Studios, where every camera is so equipped. Paramount also 
has several of similar design, as no doubt have other studios, but 
MGM, through their chief cinematographer, John Arnold, have 
stressed the importance of this tool. The improved finder is void of 
lost motion, exactly correlating the focus and fields of the camera and 
finder lenses, respectively, greatly facilitating the speed and acH 
curacy of the camera crew. 

A rather unique set-up is the dual screen transparency camera,! 
devised by Farciot Edouart and the Transparency Department of| 


Paramount Studio (Fig. 1). It augments projection background 
work by doubly widening the process background, and permitting 
its use by simultaneous projection on two screens of this doubled 
area. Twin cameras are mounted in such a way that they photo- 
graph a background of double the ordinary width as reflected on sur- 
face reflectors adjusted to simulate a single background. This makes 
possible, for instance, continuity of action across two screens (or a 
screen of double width) ; the exact alignment of horizon levels on the 
two screens; no lap-overs at their junction; and the maintenance of 
the size of actors or objects found in the single screen. 

Although designed for and adapted to Technicolor and cartoon 
work, the new Disney multiplane camera is an outstanding achieve- 
ment, with possibilities in the black-and-white field, particularly in 
title work. The camera, specially designed, is mounted to shoot 
vertically downward from the top of a chassis carrying several planes 
on which the action is depicted, each supplementing the others as 
desired. The machine is of extreme accuracy; each of the planes 
may be moved separately or jointly, with vernier calibrations assur- 
ing exactness of duplication when necessary. Since each plane may 
be lighted separately, or moved closer to or further from the shooting 
lens, or at different speeds, some of its possibilities are evident. It 
does the work in the Disney Studio of a Special Effects Department 
in the Major Studios, plus a speeding up of production due to the 
photographing of the several planes simultaneously. Because of the 
various planes, truer perspective may be achieved as the camera 
"dollies" up to or away from the "key" plane, while "atmosphere" 
is varied at will by altering the focal distances of the planes. Another 
of its manifold uses is the substitution of a "projection" background 
for one of the planes, enabling the operator to double in effects 
(shimmer, ripples, heat waves, etc.) in conjunction with the other 
planes. The Old Mill and Snow White contain examples of this multi- 
plane work. 

(3) Stage Illumination. The two Mazda lamp manufacturers 
announced as of March 1st two new photoflash lamps, the No. 7, 
which incorporates a fine aluminum wire and a small amount of foil 
in the A-15 bulb; and the No. 15, which employs special heat-treated 
foil in the A-19 bulb. The No. 7 has a total light output of 22,500 
lumen-seconds and the No. 15, 30,000 lumen-seconds. Because of 
the aluminum wire and the specially treated foil the light-output vs. 
time relation is much broader than the older, regular foil lamps. The 


advantage of this broader peak characteristic is to improve the re- 
liability of obtaining pictures when the lamps are used with syn- 
chronizing equipment. The broader flash also affords more prac- 
tical synchronism with focal-plane type shutters. The No. 7 lamp, 
being in the A-15 bulb, has also the advantage of greater compact- 

The Libbey-Owens-Ford Glass Company of Toledo, through coop- 
eration with the Nela Park Engineering Department of the General 
Electric Company and with the Technicolor Motion Picture Corpora- 
tion, has made available a special blue glass filter which, when used 
with incandescent lamps of the CP type, corrects their light so as to 
give correct color with the Technicolor process. The light emitted by 
incandescent lighting equipment employing the CP lamps and these 
niters is such a close duplication of daylight that subjects can be il- 
luminated with a mixture of this filtered light and daylight or arc 
light and no difference in the color can be detected . The filters con- 
sist of a base of medium-blue glass upon which has been sprayed a 
magenta-blue enamel, which is subsequently fired into the glass. 
This process has the advantage also of greatly strengthening the 
glass so that the likelihood of breakage is extremely remote. These 
filters had their first general introduction in the photography of 
The Goldwyn Follies and are being used in subsequent productions. 

(B) Substandard 

Keeping step with the pace set in immediately preceding years 
1937 has actively contributed to advancements in the substandard 
field of cinematography. Much new equipment of improved design 
has made its appearance, both of domestic and European manufac- 
ture. Both 8-mm. and 16-mm. equipment retain their popularity in 
America, while in addition to these sizes the 9.5-mm. equipment con- 
tinues its popularity abroad ; although it is not favorably received in 
this country. Sixteen-mm. sound equipment of improved and sim- 
plified design has done much to popularize 16-mm. film in the educa- 
tional, entertainment, and advertisement fields. Sound projection 
equipment of satisfactory quality, while still somewhat too expensive 
to find favor with the average amateur, is being slowly reduced in 
price and is now beginning to attract the attention of the advanced 

For commercial entertainment 16-mm. film has not found exten- 



sive use in America as yet; abroad in England and the Continent 
numerous theaters operate regularly with 16-mm. film. Gaumont 
British are currently releasing productions on both 35-mm. and 16- 
mm. widths. Except for the late productions of a few major pro- 
ducers, 16-mm. library films are restricted to old pictures of indepen- 
dent producers. 

Improvements in sound recording technic, advancements in the 
art of animation, refinements, and simplification of projection mecha- 
nisms have contributed in popularizing 16-mm. film for educational 
purposes. The field of visual education has grown so rapidly that 
producers of educational films have not been able to keep up with the 
demand for them. In science, in 
medicine, in industry, and in sport 
this substandard film medium is 
proving more and more important. 

(1) Films. Superpan Negative, 
new type, replaced the former 
Superpan manufactured by the Agfa 
Ansco Corporation. The new film is 
approximately twice as fast as the 
former Superpan. The film has the 
same type of color-sensitivity and 
latitude, and the grain size has not 
been increased. 

Dufaycolor film has been im- 
proved. The reseau has been made 
finer, resulting in a decided improve- 
ment in appearance of the screen 
pattern and assuring sharper definition. Dufaycolor has been made 
available abroad for 9.5-mm. cameras. The film is supplied in maga- 
zines in 30-ft. lengths. 

(2) Cameras. The new Cine Kodak model E was brought out by 
the Eastman Kodak Company. It is a moderately priced camera 
equipped with //3. 5 lens and variable speeds of 16, 32, and 64 frames 
per second. It takes either 50-ft. or 100-ft. rolls of film. 

Bell & Howell Co. introduced a new "streamlined" 8-mm. camera 
(Fig. 2), differing from former models in the design of the exposure 
dial and in the shutter release mechanism. The new models incor- 
porate single-frame exposure devices as standard equipment. 

Agfa abroad introduced the 8-mm. Movex. The camera is of the 

FIG. 2. Bell & Howell 8-mm. 



It is 

magazine type, each magazine holding 33 ft. of 8-mm. film, 
equipped with an//2.8 fixed-focus lens. 

The model F 16-mm. Siemens camera, introduced by Siemens- 
Halske, is of the magazine type and follows the well established line 
of Siemens equipment. It has interchangeable lenses and the lenses 
are provided with focal lengths from 20 to 200 mm. The camera has 

FIG. 3. Victor model 38. 

four speeds, 8, 16, 24, and 64, and is equipped with a single-frame 
device for making still pictures. This camera is being imported for 
the American market. Siemens also introduced an 8-mm. camera 
taking 25-ft. spools of double-^ film. The speed control is coupled 
with the aperture. Four speeds have been provided. The camera 
is also equipped with a single-picture device. 

Zeiss Ikon abroad brought out the Movikon 8. The camera is 
equipped with an //2 Zeiss lens. Features of the camera are inter- 
changeable lenses and film speeds of 8, 16, and 64 frames a second. 



This camera is said to be the first precision-built camera to accommo- 
date both single 8-mm. and double-^ film. 

Ditmar, a 9.5-mm. camera made in Austria, was announced to the 
European trade. The camera is equipped with an//2.9 Cassar lens, 
has an interchangeable lens mount and two speeds. This Company 
also introduced a new 8-mm. camera. 

Pathe abroad introduced a new 9.5-mm. camera, equipped with a 
fixed-focus //2. 5 lens. The camera is claimed to be unusually silent 
and is said to be the smallest movie camera made. 

FIG. 4. Victor model 33. 

(3) Projectors. The Animatophone model 38 (Fig. 3), a 16-mm. 
sound projector, was introduced by the Victor Animatograph Cor- 
poration. It is regularly equipped with two 12-inch magnetic type 
speakers and delivers 30 watts of undistorted output. The use of 
permanent-magnet speakers makes it possible to use four speaker 
units when desired to insure better sound distribution. The equip- 
ment is suitable for large auditoriums. In addition, a mixing panel 
has been provided for educational purposes and classroom use, which 
permits the instructor to add his own comments by eliminating the 
sound without having to readjust the volume or tone of the amplifier. 
Victor Animatograph Corp. also brought out a model 33 Animato- 
phone (Fig. 4), a small, compact, low-priced 16-mm. sound projector. 



The speaker and projector are combined in one unit for portability. 
A 5-watt output amplifier is provided. The lamp house has spira- 
draft ventilation and is adaptable to all standard prefocus projec- 
tion lamps. 

FIG. 5. 

Sound Kodascope Special; set up with 
1600-ft. reels. 

The sound Kodascope Special (Fig. 5) was introduced by the 
Eastman Kodak Company. This instrument represents years of 
research in the development of 16-mm. sound equipment and is a 
radical departure from the usual 16-mm. sound projection apparatus. 
Operation of the equipment is extremely simple. An automatic 
loop-forming mechanism assures synchronism. The scanning-drum 
shaft carries a flywheel and is driven by viscous coupling. In this 


way any possibility of high- or low-frequency modulation is avoided. 
The pull-down is of the single-claw type, and is designed to have low 
acceleration at both ends of the stroke. The entire mechanism is 
enclosed in an oil-bath which insures long mechanical quietness. 
Films may be projected at 24 or 16 frames per second. An //1. 6 
2-inch lens is supplied as standard equipment, and a 4-inch //1. 6 lens 
is also available. Reel arms are provided for 1600-ft. reels. A lever 
changes the focus of the high aperture scanning-beam so that re- 

FIG. 6. The 138- J Filmosound and the 138- J with booster amplifier. 

versible films, positive prints, or reversible duplicates may be pro- 
jected without loss of frequency response. The pre-amplifier is in- 
stalled in the base of the Kodascope and the power amplifier is con- 
tained in the speaker assembly. 

The Filmosound model 138, manufactured by Bell & Ho well, has 
been much improved. A reversing switch has been provided as well 
as a still-picture clutch. In addition to the single-case machine, a 
two-case model is now offered, one of the cases being the projector 
blimp and the other housing the loud speaker. For installations where 
volume greater than can be provided by the 1 38 model is necessary, 



a special speaker case housing a power amplifier is available (Fig. 6) . 
With this arrangement sufficient volume can be obtained for large 
auditoriums. The model 120 Filmosound is also now equipped with 
a reverse switch and still-picture clutch. A new amplifier for the 
equipment has been designed which provides 25 watts of undistorted 
output. High-fidelity permanent-magnet dynamic speakers are 
now furnished with this equipment. The power output of the 
Filmosound model 130 (Fig. 7) has been increased to an output of 

FIG. 7. Model 130- D Filmosound. 

50 Watts when two speakers are used. The volume is said to be more 
than sufficient for average auditorium use. 

The Ampro Corporation brought out a new 16-mm. sound pro- 
jector, model L (Fig. 8). The projector is equipped with a barrel 
type of shutter and a 750- watt lamp. It provides sufficient illumina- 
tion for auditorium projection. The amplifier output is 40 watts 
undistorted power to two speakers. 

Standard Projectors, Inc., introduced anew 16-mm., 750-watt pro- 
jector employing a barrel type of shutter and an //1. 6 lens. An in- 
teresting novelty is the adjustable gate tension which makes it 
possible to project any type of film with safety. 



Eastman Kodak Co. introduced an 8-mm. Kodascope model 50. 
This is a projector in the medium-price range. 

S. P. Equipment, Ltd., brought out a new 16-mm. sound projector 
making use of an intermittent sprocket instead of the customary 
claw for moving the 16-mm. film. The film is moved over a 6-tooth 
sprocket which insures smooth film operation even with damaged 

FIG. 8. Ampro model L sound projector (16-mm, 


Abroad, Paillard-Bolex improved their line of universal projection 
equipment for projecting interchangeably 8, 9.5, and 16-mm. films by 
introducing the interchangeable condensers so that maximum il- 
lumination would be obtained with whatever width of film was being 

Agfa abroad introduced the Movector 8. A 200-watt lamp with 
specially designed condensers is claimed to give excellent illumination. 

(4) Miscellaneous. A cine exposure meter was brought out by 
Weston. The meter has a viewing angle of 25 degrees, which is ap- 
proximately that of a 1-inch lens. 



A new wide-angle lens for all 16-mm. Cine Kodaks was made avail- 
able by the Eastman Kodak Company (Fig. 9). The lens has a focal 
length of 15 mm. and an//2.7 lens in a focusing mount. The focus- 
ing scale is graduated down to 6 inches which makes the lens especially 
useful for close-up cinematography. 

A new auxiliary condenser to be used on all current model Bell & 
Howell projectors, except the model 130, was brought out by Bell 
and Howell (Fig. 10). This condenser is inserted in a slot provided 
in the rear of the regular condenser in the equipment. Its use is said 
to increase the illumination as much as 56 per cent when wide-angle 
lenses or lenses of wide aperture are being used. 

A new exposure guide for 
Kodachrome film was brought 
out by the Eastman Kodak 
Company (Fig. 11) to assist users 
of this film in obtaining correct 


(1) General. The trend toward 
mobile recording equipment has 
been brought about by a desire 
to use equipment interchange- 
ably for stage and location work, 
and by the advantages of having 
channel-operating personnel more 
intimately associated with stage production. It is further em- 
phasized by the new sound-stage construction that makes de- 
centralization of the recording plant more necessary. Twentieth 
Century-Fox have added a number of channels employing trucks in 
which the recording equipment is located. A portable mixer is 
carried to the set, and connects to the truck for recording. 
Metro-Goldwyn-Mayer have added stage units, dolly-mounted, 
which contain complete channels from mixer to recorder. These are 
operated on the stage adjacent to the set, and require only connection 
to the 110-volt a-c. lines for power. General Service Studios mount 
their recording equipment in trailers (Fig. 12), and carry a portable 
mixer unit to the set. In addition, they have trailer-mounted re- 
recording machines that may be used in conjunction with either fixed 
or mobile recording channels for re-recording. Such a set-up usually 

FIG. 9. Kodak 15-mm. f/2.7 lens. 



olves the use of a review room or small stage for monitoring and 
projection facilities. Paramount employs stage units or "teawagons" 
on the set, connected to a central recording building housing the re- 
corders and associated equipment. 2 

Increased emphasis has been placed upon recording methods pro- 
viding improved quality and greater volume range. Methods in- 
clude: non-slip printing; intercutting of variable-width and vari- 
able-density sound-tracks; the use of track-squeezing devices with 
variable-density recordings; and the application of a new form of 
pre- and post-equalization to variable-density push-pull records. 
The latter method was introduced by Metro-Goldwyn-Mayer, and 

FIG. 10. Magnilite condenser. 

results in additional noise reduction, decreased intermodulation, and 
elimination of background noise modulation or "hush-hush." 

Multichannel recording for musical scoring is an interesting varia- 
tion of the usual scoring technic. Separate channels are used for the 
soloist, orchestra, or chorus. As much acoustic separation as possible 
is employed between the different microphones. This method 
makes it possible to record all parts simultaneously, effecting some 
recording economies. The separate tracks are then available for 
re-recording in the usual way. In exceptional circumstances, notably 
in Universal's 100 Men and a Girl, separate channels were used to 
record different instrumental groups of an orchestra. 

(2) Equipment. A number of novel devices based upon advanced 
engineering principles have been announced during the past year. 
Electrical Research Products, Inc., have developed a negative play- 
back amplifier suitable for reproducing directly from film negatives 3 



(Fig. 13). Applications include editing and re-recording newsreels, 
and studio facilities for reproducing from negatives when it is desired 
to compare sound quality from negatives and prints. 


16 MM. 8 MM. 



FIG. 11. Kodachrome exposure guide for type A film 
in photoflood light. 

A new type of hill-and-dale recorder utilizing reverse feedback was 
announced by Bell Telephone Laboratories. 4 In addition to im- 
proved quality for processed recording materials, it provides ex- 
cellent recordings on direct materials for immediate playback. It 
has wide application for scoring for playback work. 

RCA has developed a new modulator system capable of recording 



variable-width or variable-density tracks, either standard or push- 
pull. 5 

A large number of RCA recorders of both studio and portable 
types manufactured and in service before the advent of ultraviolet 
recording and the bilateral shutter 6 were equipped to include these 
recent developments. 

The non-slip 7 printer developed by RCA has come into more gen- 

FIG. 12. Trailer recording unit. 

eral use during the past year. Printers utilizing the principle are 
being produced commercially and the industry has come to use non- 
slip prints as the standard of comparison. A motor-driven blooping 
shutter has been added to a number of RCA printers with very satis- 
factory results. 

Class A push-pull recording 8 was demonstrated very successfully 
in a series of tests. Due to its numerous advantages, such as can- 
cellation of even-harmonic distortion, elimination of splice noises, 
speeding up of noise-reduction shutter action, and elimination of 
shutter thump usually resulting from this increased speed of action, 



etc., a number of recordings have been made under routine studio 

The development of the modulated-carrier oscillator 9 has provided 
an excellent means for determining the optimal processing conditions 
for variable- width recordings. Continued use of this oscillator in 
making recordings for a number of processing laboratories during the 
past eighteen months has demonstrated the value of this instrument. 

FIG. 13. Negative playback unit. 

A newsreel type of recording equipment was introduced by RCA. 
This equipment provides class B push-pull recording with ultraviolet 
light on the identical film upon which the picture is photographed. 
The recording optical system is mounted on the rear of the motion 
picture camera. Although light in weight and simple to operate, 
this equipment includes features heretofore obtained only in studio 
type apparatus, and produces results that compare favorably with 
studio recordings. 


(3) Accessories. The General Radio Company brought out a new 
power-level indicator, a vacuum-tube type rather than copper-oxide, 
which they had previously manufactured (Fig. 14). This instru- 
ment has a high-speed meter with a delay circuit so that sudden peaks 
are not lost but are indicated quite faithfully. A delay circuit makes 
the return swing much slower than that provided by the meter move- 
ment itself, with the result that the indication seems to float on peaks 
and gives an accurate monitoring indication without the erratic 
motion characteristic of high-speed instruments. 

The Mole-Richardson Co. has developed the type 103-B microphone 
boom and type 126-B microphone boom perambulator (Fig. 15). 
The wide use of the new light-weight microphones indicated that it 
was advisable to use duralumin and light-weight aluminum alloys in 

FIG. 14. Type 686-A power-level indicator. 

the construction of the new boom head. In analyzing the causes 
of noise in boom operation it was decided to eliminate the use of 
stranded -wire cable, to put all moving parts on rolling rather than 
sliding contact surfaces, and as the design was developed a means 
was worked out of supporting the telescoping tubes on rubber rollers. 
Incorporated in the design as an integral part is the complete gunning 
device which rotates the microphone through 280 degrees. The 
weights of the various components are indicated in the specifications. 
The microphone boom perambulator is of the three-wheel type, 
which facilitates maneuvering, and is designed so that the wheel 
tread can be narrowed to pass the perambulator through a 30-inch 
door and can be widened to provide a substantial working base. The 
column and supporting platform for the operator are simultaneously 
elevated or lowered by means of a screw-operated lifting system. 
Careful attention has been given in the design of the perambulator to 
the elimination of all extraneous noise. 



Other equipment introduced during the past year that tends to 
improve or facilitate recording includes the miniature condenser 
transmitter, high-quality moving-coil head-sets for monitoring on the 
set, and various forms of the peak volume indicator. 10 ' 11 All these 
devices require some change in studio operating technic to realize 
their full advantages. 

Routine transmission testing has been greatly facilitated by the 
use of recording types of gain-measuring apparatus. 12 This method 
gives records that are useful for immediate inspection and subse- 
quent filing, and minimizes maintenance costs. 

FIG. 15. 

Type 103-B microphone boom and type 126-B microphone boom 

A new method of determining correct negative and print densities 
utilizing a modulated high-frequency oscillator has been described 
by RCA. 13 

The Academy of Motion Picture Arts & Sciences has continued 
with its program of standardization, and has recommended a number 
of standards for theater electrical characteristics, dividing networks, 
filters, and other allied subjects. 

(4) Films. The Eastman Kodak Company announced a new 
fine-grain, high-contrast film, designated as E.K. 1360, for variable- 
width recording. It is claimed that white light may be used with 
this emulsion with results as good as or superior to that obtained with 



ultraviolet light and standard positive emulsions. It is also claimed 
that this film is very quiet in projection and has high resolving power. 
The Dupont Film Manufacturing Corporation announced two new 
sound recording films during 1937, types 214 and 215, which replace 
the former 201 and 202 types. The new films retain the desirable 



M AOR1D"& "WiNlCS 


FIG. 16. 

Glass blocks with lights of various colors 
behind them. 

emulsion characteristics of the former types and differ only in that 
they are manufactured by a newly perfected technic that eliminates 
the periodic density fluctuations characteristic of all films manufac- 
tured in the conventional manner. This results in a more steady 
ouput, especially from variable-density films, as is easily observed 
in the reproduction of constant-frequency films. 




The past year has been peculiarly barren in the production of new 
types of sound-picture projection equipment. Many theaters have 
been modernized with the various equipments described in last year's 
report. The Academy of Motion Picture Arts & Sciences has labored 

FIG. 17. Changeable-letter sign with extended back- 
ground to allow use of letters of a variety of sizes. 

hard to effect standardization of reproducer characteristics and has 
issued information on the subject during the year. 14 

(1) Motion Picture Theater Lighting. In view of the many interest- 
ing advances in theater lighting equipment and technic the Committee 
is including in this report for the first time information on this topic. 

Two important developments have occurred during the past year 
to make it possible to lift the shroud of darkness that has covered 


motion picture theater audiences: (1) The efforts of the National 
Carbon Co. to increase the prevailing levels of screen illumination 
through the use of the newer carbons, thus making possible moderate 
increases in the general level of the auditorium illumination. This 
was done by conducting a campaign throughout the industry for 
greater screen brightness. (2) More important still, the widespread 
use of down lights mounted above the ceiling of the auditorium and 
projecting a well defined beam of light through a 2-inch hole toward 
the front of the auditorium. Thus is provided ample general audi- 
torium illumination for patrons to move about and read their pro- 
grams ; and at the same time the decorative colored lighting, which is 
often of a low order of brightness, as well as the contrasts on the 
screen, is not destroyed. 

Considerable progress has been made also in the use of polished 
fluted metal reflectors for both decorative and exterior lighting. 
These reflectors may employ either individual incandescent lamps or 
neon tubes. They have the effect in many instances of apparently 
creating many more sources than are actually present. 

There has been a more widespread use of the luminous treatment 
of theater fronts and marquees. These comprise the use of glass 
blocks as well as luminous panels and polished metal illuminated by 
projected light. The use of these developments is shown in the photo- 
graphs of the Cine Theater (Fig. 16). The changeable-letter sil- 
houette sign, previously reported, has been expanded to permit the 
use of a variety of letter sizes and thus obtain greater emphasis. 
The illustration showing the Rhodes Theater (Lost Horizon) demon- 
strates this feature (Fig. 17). 

Theater interiors are receiving the same general treatment as the 
outside in that there is more general use of luminous panels and deco- 
rated glass blocks, behind which lamps of various colors are placed. 

(2) Theater Lighting Equipment. For theater use there has re- 
cently been made available a 500- watt, 115-volt, T-14 bulb, biplane- 
filament, medium-bipost base lamp for elliptical spots and down- 
lights. This lamp is unusual in that the highly concentrated light- 
source is placed relatively near the end of the bulb and the lamp is 
intended for base-up operation. This design results in a minimum of 
obstruction of the light from the reflector by the lamp bulb. 

Two stage-lighting equipment manufacturers have developed a 
Fresnel-lens spot somewhat similar to those introduced a few years 
ago for motion picture set lighting. These are to be used for theater 



spots and general stage lights. Another equipment manufacturer 
has placed upon the market an end -seat lighting unit, which consists 
of a decorated luminous panel to provide aisle illumination. 

(3) Accessories. About two years ago the Mazda lamp manu- 
facturers introduced a general service lamp having an anti-blackening 
screen mounted above the filament, upon which the tungsten evapo- 
rated from the filament was deposited. During the past year there 
_ has been made available a 1000-watt, T-12 bulb, 

concentrated-filament projection lamp incorporat- 
ing a similar anti-blackening screen (Fig. 18). 
The amount of blackening reaching the bulb is 
thus reduced to the extent of improving the candle- 
power maintenance during life 30 per cent over that 
of a lamp not equipped with this device. 


The growing interest in the use of motion pic- 
tures in education was shown by the introduction 
of a new publication, Motion Pictures of the World. 
This is a quarterly publication issued by Inter- 
national Educational Pictures, Inc., Boston, and 
is stated to contain a list of all new pictures 
released in the preceding three months. World 
Film News (Cinema Contact, Ltd., London) made 
its de"but during 1937. Current pictures are re- 
viewed, studio activities discussed, progress in the 
documentary film treated, and television develop- 
ments noted. It is a pleasure to note that the 
British Kinematograph Society has been able to 
replace their Proceedings by a Journal, of which 
the first number made its appearance in 

December, 1937. 

Since the last report of the Committee in May, 1937, the following 

books of noteworthy interest have appeared: 

(1) Motion Picture Sound Engineering (chapters by various authors), Academy 
of Motion Picture Arts & Sciences, Hollywood, Calif. 

(2) Sound Recording for Films; W. F. Elliott, Pitman & Sons, Ltd., London. 
(5) Talking Pictures; B. C. Kiesling, Johnson Publishing Co., New York, N. Y. 
(4) Sound Motion Pictures and Servicing Sound Equipment; J. R. Cameron, 

Cameron Publishing Co., Woodmont, Conn. 

FIG. 18. 1000- 
watt standard- 
voltage, T-12 
bulb projection 
lamp with col- 
lector grids. 


(5) Entwicklung der Kinotechnik (Development of Motion Picture Technic); 
R. Thun, VDI Verlag, Berlin. 

(6) Amateur Movies and How to Make Them; A. Strasser, Studio, Ltd., 

(7) How to Write a Movie; A. L. Gale, Brick Row Book Shop, New York, N. Y. 

(8) Film and School; H. Rand and R. Lewis, Appleton Century Co., New York, 

(9) Motion Pictures in Education; Compiled by E. Dale, F. W. Dunn, C. F. 
L, Jr., and E. Schneider; The H. W. Wilson Co., New York, N. Y. 

Camera Lenses and Shutters; R. M. Fanstone, British Periodicals, Ltd., 

(11) Camera Lenses, 2nd Edition; A. Lockett, revised by H. W. Lee, Pitman 
publishing Corp., New York, N. Y. 

(12) Home Movie Gadgets; W. J. Shannon, Moor field & Shannon, Nutley, 

(13) Exposing Cine Film; P. C. Smethurst, Link House Publications, Ltd., 

(14) The Secrets of Trick Photography; O. R. Croy, translated by P. C. 
Smethhurst, American Photographic Publishing Co., Boston, Mass. 

(15) Film Making from Script to Screen; A. Buchanan, Faber and Faber, Ltd., 

(16) Titeltechnik (Title Technic) ; F. Lullack, W. Knapp, Halle, Germany. 

(17) Mein Weg mit dem Film (My Experience with the Film); O. Messter, 
M. Hess, Berlin-Schonberg. 

(18) Technique of Color Photography, 2nd Edition; F. R. Newens, Blackie & 
Son, Ltd., London. 

(19) Picturing Miracles of Plant and Animal Life; A. C. Pillsbury, Lippincott 
Co., Philadelphia, Pa. 

(20) Photography Theory and Practice, 2nd English Edition; Pitman Pub- 
lishing Co., New York, N. Y. 

(21) Lichtspieltheater, Anlage und Einrichtung (Planning and Equipping a 
Motion Picture Theater); Bauwelt-Encyclopedia Vol. 9, Bauwelt-Verlag, Berlin. 

(22) We Make the Movies, edited by Nancy Naumberg, W. W. Norton & Co., 
Ind., New York, N. Y. 

Yearbooks were issued by the following publishers: 

(1) Quigley Publishing Co., New York, N. Y. 

(2) Film Daily, New York, N. Y. 

(3) Kinematograph Publications, Ltd., London. 

(4) Photokino- Verlag, Berlin. 

(5) M. Hess, Berlin-Schonberg. 

Abridgments and collections of original papers were published as 
follows : 

Abridged Scientific Publications of the Kodak Research Laboratories, 17 
(1935), Eastman Kodak Co., Rochester, N. Y. 

Veroffentlichungen des wissenschaftlichen Zentral-Laboratoriums der Photo- 
Ateilung Agfa (Publications of the Afga Central Photographic Research 
Laboratories), 5, Hirzel, Leipzig. 


(All references are to J. Soc. Mot. Pict. Eng. unless otherwise noted) 

1 IVES, C. E., AND CRABTREE, J. I. : "Two New Films for Duplicating Work," 
XXIX (Sept., 1937), No. 3, p. 317. 

*GRIGNON, L. D.: "Light- Weight Stage Pick-Up Equipment," XXIX (Aug., 
1937), No. 2, p. 191. 

'ALBERSHEIM, W. J.: "A Device for Direct Reproduction from Variable- 
Density Sound Negatives," XXIX (Sept., 1937), No. 3, p. 274. 

4 VEITH, L., AND WIEBUSCH, C. F.: "Recent Developments in Hill-and-Dale 
Recorders," XXX (Jan., 1938), No. 1, p. 96. 

5 DIMMICK, G. L.: "The RCA System and Its Application to Various Types 
of Sound-Track," XXIX (Sept., 1937), No. 3, p. 258. 

6 HASBROUCK, H. J., BAKER, J. O., AND BATSEL, C. N.: "Improved Noise- 
Reduction System for High-Fidelity Recording," XXIX (Sept., 1937), No. 3, 
p. 310. 

7 BATSEL, C. N.: "A Non-Slip Sound Printer," XXIII (Aug., 1934), No. 2, 
p. 100. 

8 Cf. ref. 5. 

9 BAKER, J. O., AND ROBINSON, D. H.: "Modulated High-Frequency Record- 
ing as a Means of Determining Conditions for Optimal Processing," XXX (Jan., 
1938), No. 1, p. 3. 

10 HOPPER, F. L.: "Power Level Indicators for Sound Recording," XXDI 
(Aug., 1937), No. 2, p. 184. 

U ALBIN, F. G.: "A Linear Decibel-Scale Volume Indicator," XXK (Nov., 
1937), No. 5, 489. 

12 Symposium on Transmission Meters (Spring, 1937, Convention): 
LINDSAY, W. W.: "A Transmission Measuring System Utilizing a Graphic 

Recording Meter," XXIX (July, 1937), No. 1, p. 68. 

MACLEOD, A. D.: "An Automatic Audio-Frequency Graphic Recorder," 
XXIX (Dec., 1937), No. 6, p. 663. 

HILLIARD, J. K., AND SpRAGUE, G. M.: "A Continuous Level Recorder for 
Routine Studio and Theater Measurements," XXIX (Dec., 1937), No. 6, p. 645. 

AICHOLTZ, L. A.: "A Curve-Plotting Transmission Meter," XXIX (Dec., 
1937), No. 6, p. 655. 

GRIGNON, L. D.: "A Curve-Plotting Transmission Meter," XXIX (Dec., 
1937), No. 6, p. 660. 

13 Cf. ref. 9. 

14 "Standard Electric Characteristic for Two- Way Reproducing Systems in 
Theaters," Bulletin, Academy of Motion Picture Arts & Sciences, June 8, 1937; 
Hollywood, Calif. 



The year 1937, while not during its course regarded as an eventful 
year for the motion picture industry of Japan, will be remembered 
because it witnessed the enactment of several governmental regula- 


tions that will have increasing effect upon the industry during en- 
suing years. Early in the year Japan found it necessary to overcome 
her unfavorable balance of trade by an exchange control measure 
that has steadily become more stringent. Japan's deficiency in 
natural resources made the application of this measure the more re- 
strictive when the China "Incident" made the purchase of war mate- 
rials a vital necessity. It was only natural then that certain im- 
portations would be classified as nonessential in the face of the na- 
tional emergency. Unfortunately, motion picture raw film and 
foreign motion pictures fell into this category. Notwithstanding 
the fact that certain governmental groups consider Japanese-made 
motion pictures and newsreels a valuable vehicle for the internal dif- 
fusion of propaganda pertaining to the Incident, the supply of im- 
ported raw stocks has been cut drastically; in fact, to a point where 
it is questionable whether the local manufacturers can supply the 

As mentioned above, the importation of foreign pictures suffered 
under these exchange control measures. This fact, however, except 
for a few newspaper and magazine articles, did not come to the 
public's attention because foreign distributors began during the au- 
tumn to distribute their supplies of previously imported but unre- 
leased pictures. This procedure made possible the distribution of 
practically the same number of foreign pictures in 1937 as during 
the previous year, but it certainly did not allow the year to fulfill 
financially its earlier promises. Approximately 300 foreign pictures 
were released in Japan during 1937, of which about 25 per cent com- 
prised pictures from European studios. It will be noticed that Euro- 
pean productions seem to be steadily gaining ground against Ameri- 
can pictures, but this does not necessarily imply they are gaining 
popularity. Pictures produced under the social and political re- 
straint peculiar to European countries are much more likely to find 
favor in the eyes of the Japanese censors, especially in view of govern- 
mental amity. Also it must be borne in mind that the exhibitor is 
able to make more favorable terms for these pictures than for the 
American pictures. The average American picture, however, is still 
the better box-office success, especially in the large city theaters that 
make a specialty of showing foreign films. 

It is estimated that in 1937 about 600 Japanese-made pictures of 
the entertainment type were released. This includes features, come- 
dies, and shorts. There is still an appreciable number of silent pic- 


tures made expressly for the small country theaters not equipped for 
sound. Incidentally, these theaters still employ the benshi (narrator) 
to explain the action of the picture to the audience. These unscored 
pictures average only about 5 or 6 prints per picture as compared to 
the 10 to 12 prints made for each sound picture. On the basis of 
released footage there were better than 4 feet of sound-film released 
to every foot of silent film. The writer believes the total released 
footage approximated 50 million feet in 1937. About 50 per cent of 
the productions are still of the historical type. A possible reason for 
the sustained popularity of these classical plays is the fact that 
foreign releases provide the modern style picture on a scale upon 
which it is difficult for the local producers to compete. 

There was considerable activity in the production of documentary 
and educational films. Governmental agencies, newspapers, uni- 
versities, and cultural societies as well as the motion picture com- 
panies participated in making some 250 such pictures. Since, how- 
ever, these films were made primarily for private distribution, figures 
as to the lengths and subjects are difficult to obtain. The following 
classifications, however, will cover probably 80 per cent of these 
films: tourist, industrial, propaganda, educational, sport, and 

The China Incident introduced into Japan an unprecedented in- 
terest in news films. Almost overnight newsreel theaters sprang into 
existence in the large cities. These theaters are small, accommodat- 
ing only 200 or 300 persons and offer a 1 to 1 V2-hour program made 
up primarily of newsreels with one or two shorts. News of the In- 
cident monopolizes the screen to such an extent that at this early 
date when the spectacular Chinese news is diminishing in volume 
consternation is already arising as to just what to do with many of 
these theaters after the Incident is closed. 

The construction of many new theaters was completed last year. 
Two large first-class theaters, one in Tokyo (the Kokusai Gekijo) and 
one in Osaka (the Umeda Gekijo) were built by the Shochiku interests 
and Toho interests, respectively. Both theaters are equipped with 
Western Electric sound reproducing equipment. The Kokusai 
Gekijo is without doubt the largest theater in Japan and perhaps one 
of the largest in the world. It has a total seating capacity of about 
3000. The new theaters are being built with the proper acoustical 
considerations incorporated in the design and construction materials, 
a matter that previously had been given little thought. 


At this point it may be interesting to point out a few pertinent 
facts about theaters and attendance. In point of view of attendance, 
last year set a record, with a figure approaching 300,000,000 paid 
admissions. There are about 1400 theaters in Japan, 1100 of which 
show Japanese films exclusively, the remainder having mixed or all- 
foreign programs. Needless to say, the latter group are concentrated 
in the large cities. About 85 per cent of the theaters are equipped 
for sound, but only the larger theaters have invested in imported 
equipment; Western Electric leads with more than 130 theater in- 
stallations. It can be seen from the above figures that by far the 
major portion of the sound reproducing equipments is manufactured 

Several of the studios in Japan are equipped to process their own 
films by machines: notably, J. O. Studio Co., P.C.L., Shochiku 
(Tokyo) and Nikkatsu (Tokyo). There are also several companies 
that make a business of processing film, i. e., local negatives and posi- 
tive as well as duplicates of foreign productions. Of these the largest 
is the Far East Laboratory, with eight positive and four negative 
machines of the Debrie type. Others in this field are J. O. Studio 
Co., P.C.L., K. S. Talkie, and Yokohama Cinema. The latter two 
employ machines of the Art Reeves type, and process largely Japanese 
newsreels. The majority of these machines have positive processing 
speeds of 20 to 40 feet per minute and a negative processing speed of 
5 to 10 feet per minute. For financial reasons, however, many studios 
are still processing their negative and positive films by the rack-and- 
tank systems, though at present that is true only of those interested 
in the production of silent pictures. 

The motion picture laboratories in Japan have, in the past few 
years, become conscious of the advantages to be gained from close 
sensitometric control of their processing. This is especially true of 
the laboratories employing machines, where the processing of sound 
negative has made development control a vital necessity. The East- 
man type 116 sensitometer has been universally accepted as the 
standard instrument for this control work. 

The Fuji Photo Film Company has expanded its manufacturing 
facilities in an effort to supply the raw film necessary for the local 
market, now that imported stocks are so severely restricted. Their 
products include a clear base panchromatic negative film, a positive 
film and a newly introduced sound recording film. 



As a result of experience with the magnetic oscillograph introduced 
four years ago for variable- width recording, this system has now been 

FIG. 19. Minicord modulator. 

FIG. 20. Minicord sound mechanism. 

developed in very small dimensions. Including the optics the os- 
cillograph measures only 3 X 4.5 X 8 cm. ; the weight is approxi- 
mately 200 grams; the power consumption of the lamp is 3.5 watts; 
5 milliamperes are required to operate the mirror. Fig. 19 illustrates 



the recorder known as the "Minicord" sound recorder. Variable- 
width recording may be done with this instrument without lowering 
the noise level. The amplifier and other electrical equipment have 
been reduced to a minimum of weight and space. The amplifier and 
batteries of 10-hour capacity are built into a case measuring 450 X 
130 X 390 cm. and weighing 15 kg. Fig. 20 shows the 35-mm. sound 
mechanism in comparison with a 60- watt lamp. The results at- 
tained with this apparatus may be regarded as very satisfactory. 
The small size of the apparatus makes its use possible not only in 
combination with standard film 
cameras forming a single unit, 
but also in combination with sub- 
standard film cameras. 

In the field of reproduction the 
new sound apparatus for very 
large theaters, made by the Klang- 
film Gesellschaft and called "Eu- 
ronor," is remarkable, especially 
for its very large compound loud 
speaker. The size of the latter 
is determined primarily by the 
labyrinth system which consists 
of a large membrane 50 cm. in 
diameter, a horn having a length 
of 2.6 meters, and an opening of 
4 square-meters. The efficiency 
of this labyrinth system and its 
capacity are so great that about 
12 watts of undistorted output 
may be obtained at 50 Hertz. 
Four upper cones 1.6 meters in 
length are provided for the 
medium and higher frequencies. 
Fig. 21 shows the loud speaker. 
Experience with this apparatus has proved that the extension of the 
frequency range at the lower end represents a considerable step 
toward more natural reproduction. The possibility of reproducing 
special effects (explosions, earthquakes, etc.) is, of course, con- 
siderably greater due to the high acoustical efficiency at the low 

FIG. 21. 

Klangfilm loud 




Although there has been considerable improvement in the techni- 
cal and artistic standards of British pictures, the year 1937 has been 
an unsatisfactory one for the industry. Financial interests showed a 
desire for severe retrenchment largely owing to disappointing returns 
from the 1936 program and there was a rapid falling off in the num- 
ber of pictures in active production. 

Another reason for the decline has been the general uncertainty as 
to the final results of the Government's new Films Bill, designed to 
replace the expiring Act of 1927. The main object of the bill is, 
of course, to foster the production of British films, and the Govern- 
ment, starting with the Moyne Report as a basis, has considered 
the views of all sections of the industry. Unfortunately a funda- 
mental conflict of interests has been revealed and the bill will require 
considerable modification before a compromise can be reached. 

An important function of new legislation, and one that is generally 
agreed to be desirable, would be not only to regulate the proportion 
of British films exhibited but also to set a minimum standard of 
entertainment quality and so eliminate the. damage to prestige 
caused by "quota quickies," a type of picture made more with the 
object of complying with the law than as entertainment. The 
means of achieving this quality standard is still under discussion but 
it seems likely that a minimum cost figure will be established with the 
provision that a fixed proportion will be spent on labor. 

With the American product available as a standard of comparison 
no act can guarantee that competitive films are produced, but it is 
felt that the studio facilities available in this country are ample and 
that if a reasonable compromise bill can be passed and future con- 
ditions stabilized a return of confidence will produce increased ac- 
tivity in the coming year. 

Studios. Amalgamated Studios, Elstree, were completed in the 
early part of this year. These studios comprise four large stages, 
each equipped with its own dressing rooms, cutting theater, and sound 

* Received June 21, 1938, from R. J. Engler. 


recording and monitoring facilities. Two large theaters are available 
for the combined purposes of dubbing, scoring, and reviewing. The 
sound equipment is Western Electric. Owing to the depressed state 
of the industry the studios have not yet started production. 

The Warner Brothers Studios at Teddington have been equipped 
with RCA variable-width recording facilities, which are to be con- 
verted for class A push-pull operation in the near future. 

In order to eliminate price-cutting, an agreement was reached be- 
tween the major service studios on standardizing charges to producers, 
and during the year various means, such as the making of pictures 
on a cooperative basis, have been tried to keep the studios in pro- 

Laboratories. Generally the laboratories have had a quiet year, 
although improvements in technic have occurred in some instances, 
particularly in the use of sensitometric methods of development con- 
trol and an increased use of turbulation of the developing solutions. 
Efforts to improve the quality of duplicates have led to the use of 
two new film products, Eastman fine-grain duplicating positive and 
Eastman fine-grain duplicating negative, both extensively used in the 
U.S.A. These new films differ materially from the normal duplicat- 
ing product, and require considerable modification of the printing 
equipment set aside for this work. A certain amount of tinting and 
toning of release prints was undertaken although the quantity of this 
kind of work does not seem to be increasing. Several laboratories 
are adding 35-mm. to 16-mm. sound and picture reduction printers, 
and there was an increase in the use of 16-mm. prints, mainly for 
industrial purposes. 

The new Technicolor Laboratories at Harmonds worth started 
commercial operations early in 1937. By the end of the year 
they were working at full single-shift capacity and were manufactur- 
ing all British release print requirements as well as a number of 
foreign-language versions of all current Technicolor pictures pro- 
duced in England and the United States. 

Denham Laboratories, situated near London Film Production 
Studios, are now in operation and are equipped with the latest type 
of processing apparatus. Five DeBrie daylight developers are avail- 
able with seven DeBrie Duplex printers, one Bell & Howell type 
printer as well as an optical printer for special effects. A 35-mm. to 
16-mm. optical reduction printer is also installed. 

Twelve non-slip sound printers are now installed in London Labo- 


ratories and are proving valuable for re-recording copies and duplicat- 
ing work. 

Newsreels. The major event in the newsreel sphere was the re- 
cording of the coronation ceremony, particularly as permission was 
obtained from the authorities to take photographs within West 
minster Abbey. The conditions were, however, very difficult and the 
results obtained, which included several colored versions, must bt 
regarded as remarkably successful. 

British Movietonews have moved to enlarged premises in Sohc 
Square and Kay Film Laboratories have established a plant adjacenl 
so as to give an improved service. 

Technical Advance. Messrs. W. Vinten, Ltd., have developed 
step-wedge printing machine for making rising density test prim 
strips of negatives and also density strips for taking the speed or ex 
haustion of developing baths. This machine prints eleven frame* 
with one pull of a handle, and can be operated in daylight. A syn 
chronous generator ensures steadiness of the voltage on the light 
source from day to day and a special photocell is used to check th< 
color constancy of the lamp. 

The same firm has also produced a complete portable daylighi 
processing unit which can be mounted, complete with air-condition 
ing, in a moderately sized lorry. A camera taking 250 pictures t 
second and equipped with a special view-finder has also been de 
veloped to supplement the existing high-speed type. This camen 
is equipped with a 400-ft. magazine and is very light in weight. 

A new type of multiple printer is being developed capable of taking 
four 16-mm. prints from one negative at the same time. It is pro 
vided with four double-8-mm. heads interchangeable with th< 
16-mm heads. The machine can also be arranged to use four nega 
tives and take four positives when a special light control is providec 
for with separate control of each of the four printing lights. 

A 35-mm. to 16-mm. sound reduction printer is available operating 
on a dual track method with a unique system of mechanical syn 
chronization between 35-mm. and 16-mm. films. 

Exhibition. Despite the decline in the production side of the in 
dustry 1937 was an improved year for exhibitors. Extensive 
new building continues, although a campaign against overbuilding 
has been started and attempts made to include provisions against il 
in the New Films Bill. There has, however, been a halt in the 
building of news theaters and it is felt that the trade will eventuall} 


regulate new building in cooperation with the renters by refusing to 
supply films to unrecognized cinemas. 

Technical developments have been in the direction of the increased 
use of two-way horn systems with multicellular high-frequency 
units, the Western Electric Mirrophonic system having been demon- 
strated early in the year. 

Broadcasting and Television. The broadcasting of advertising 
programs intended for British listeners from certain continental 
stations continues despite proposed international legislation to limit 
it. The programs are generally recorded either on disks or by means 
of the Philips-Miller system. 

Television has made some progress in the home entertainment 
field and several successful outside broadcasts have been made, 
notably those of the coronation ceremony and several from film 
studios. The Gaumont British and British Movietonews reels con- 
tinue to be a regular part of the programs. 

As yet, however, the number of sets is estimated as only 2000, so 
that no effect is likely to be felt by the cinemas for a considerable 
time. Factors limiting a substantial increase in these numbers are 
the limit of coverage of the London area, the restricted hours of 
transmission, and the high cost of receiving sets. 

However, recent demonstrations of large-screen television by the 
Scophony and Baird systems have proved encouraging and its use in 
cinemas is being considered. Both the companies demonstrating 
are associated with large theater circuits so that the systems will 
probably be exploited as soon as technical development is sufficiently 
advanced. The future of television in motion picture theaters will 
depend upon several factors that are at present doubtful. Among 
these are the questions of the copyright of the B.B.C. television 
transmission and the possibility of providing programs, suitable for 
showing in cinemas, either by the B.B.C. or some separate organiza- 
tion. The latter would, of course, entail the erection of special 
radio transmitting stations or the provision of suitable cable distribu- 
tion networks. 



Summary. In connection with the general improvement in cartoon technic, 
it was recognized that several developments could be undertaken that would add much, 
if successfully adapted, to the power and charm of animated motion pictures. By 
confining cartoon photography to a single plane in front of the camera, the expense 
and difficulty of creating a convincing illusion of depth and a real-life appearance 
by camera movement made the consideration of a multiplane technic imperative. 
The out-of-focus diffusion and the differential movement of foreground and back- 
ground of scenes can be achieved most easily by separating the elements on different 
planes in front of the camera. The problem resolved itself into the adaptation of 
glass-shot technic to cartoon production. In separating the scene elements into 
several planes, many other advantages were gained, such as lighting control of single- 
scene elements, ease of using special effects equipment, and possibility of using back- 
light and process backgrounds. 

The answer to the problem was the multiplane camera, built with the view of ac- 
curacy of control, complete flexibility of scene set-up, and ease of operation. This 
required plane elements that could be quickly and accurately assembled and disas- 
sembled; separate lights for each plane; a quick-reading and accurate indicating 
system; and an interlocked system of controls. 

Because the light level on each plane is an important part of every set-up, a special 
light-measuring system had to be devised. The number of machine adjustments 
involved was so large that a master control sheet was laid out, giving complete opera- 
tion information for each frame of film. As a final check before exposure, a peri- 
scope type of finder was devised so that the chief operator could check the set-up visu- 
ally before each exposure. To write out the master control sheets, it was necessary to 
develop a scene-planning group of artists and technicians to control and plan the 
use of the machine in creating the desired illusions. 

The results in enhancing the effectiveness of animated motion pictures have been 
very satisfactory. The multiplane technic has proved so flexible that its complete 
possibilities will be realized only with experience. 

The usual cartoon technic is to photograph both character and 
background on one plane in sharp focus. The multiplane technic is 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 14, 1938. 

** Walt Disney Productions, Inc., Hollywood, Calif. 


the separation of scenes into their several foreground and background 
elements, and designing them to be photographed at different dis- 
tances in front of the camera. The camera photographs through 
these elements, which are painted on glass. On one or more of the 
elements the usual animated characters are held in register to the 
action level part of the scene. 

The advantages of using a multiple-plane technic in cartoon 
photography are manifold. An evaluation of these advantages, an 
analysis of the means of getting them, and the adaptation of these 
means into the established technic of animation, comprised the back- 
ground for the design of the multiplane crane. 

The primary problem leading to the multiplane idea was to increase 
the illusion of depth in animated motion pictures. To do this, there 
are several things, short of true stereoscopic photography, that can 
be done. Careful handling of color and painting technic will add 
much to the illusion of depth. However, the artistic problem of 
getting and controlling the out-of-focus diffusion of foreground and 
background scene elements is very difficult when whole scenes are 
shot on one plane in sharp focus. Controlling this diffusion by using 
several plane scenes and adjusting the depth of focus as desired gives 
a more convincing result. But the most important part of the ap- 
pearance of depth comes from camera movements. 

Pan shots, in cartoon parlance, refer to scenes in which the camera 
appears to travel parallel to the background. It is in pan shots that 
the real-life movement between foreground and background elements 
can best be portrayed. As the scene elements are moved rather than 
the camera in photographing the cartoon, the speed of the elements 
can be controlled as they pass in front of the camera. In the pan 
shot, therefore, the sky, the middle distance, and the foreground can 
be separated and moved at speeds that will maintain the correct 
perspective relations of the scene as originally conceived by the 
artists. While it might seem possible to paint all the elements on 
separate transparencies to be shot on one plane and still control the 
perspective by different movements, it is not practicable because the 
pile-up of transparencies will cause noticeable shadows of the top 
characters upon the bottom characters if the pile-up is more than 
0.040 inch thick. 

In a so-called truck shot, in which the camera appears to move 
toward or away from an object, a depth effect can be accomplished 
only by the use of a multiplane scene. In moving the camera along 

146 W. E. GARITY AND W. C. MCFADDEN [j. S. M. p. E. 

the lens axis, it is easily shown that the photographed fields nearest 
the camera are changed in size at a proportionally greater rate than 
those farther away. The proportional change varies inversely with 
the field size, which is exactly the condition found in real-life ob- 
servation. In multiplane scenes, it is possible to keep the very 
distant background and sky elements from changing in size during 
camera trucks by keeping them at the same distance from the camera 
while the latter is moving with respect to the characters and fore- 

Overall light changes showing transitions, such as dawn to full 
daylight in the same scene, can be done in cartoon work with fades 
or filters. But when only part of the scene requires a lighting 
change, in standard cartoon photography such a change can be done 
only by double exposures. In multiplane photography, the lighting 
changes can be achieved easily by filtering or otherwise controlling 
the light on the element to be changed. A large range of light level 
can be attained by using bulbs of diiferent wattages in the lamp- 
boxes. For smaller variations in light, a range of voltage from normal 
to 20 volts above normal can be used. This over-voltage range is 
necessarily small because of the usual limitation due to variation of 
the color of tungsten lamps with voltage. In practice it has been 
found that this voltage range is consistent with reasonable bulb life 
and color quality. At times the color variation of tungsten lamps is 
used to advantage by running them under voltage for certain effects. 

Because of the separation of scene elements, the possibilities of 
special effects are greatly increased. Distortion and diffusion glasses 
for a single background element can be used without affecting the 
rest of the scene or characters. The use of mirrors and other optical 
equipment is greatly facilitated in multiplane scenes. By careful 
planning, almost any scene can be broken down in such a way that 
control of lighting, color, and optics is achieved over any part or all 
of the scene. This control would not be at all practicable if the tech- 
nic were confined to a single plane. While animation effects are ap- 
parently unlimited, there are certain weaknesses that special-effects 
equipment circumvents. It is impracticable to paint gradual changes 
of light level or color, or to animate the slow distortion of backgrounds 
or reflections. 

As the multiplane idea necessitated transparent backing for car- 
toon characters, the door was opened to a large range of effects with 
back-lighting such as the glow around lamps, sparkles, sunsets 

Aug., 1938] 



through dark clouds, etc. Although process backgrounds have not 
been used, they are quite possible with the multiplane crane. 

From the experimental work on the multiplane idea, the necessary 
requirements for a successful camera crane were set up (Fig. 1). 
Two general types of supports for the scene elements were required. 

FIG. 1. General view of multiplane crane. 

One was the contact plane, which would handle both glass back- 
grounds and animation; and the other was the background plane, 
which would support only the glass backgrounds. However, the 
desire for freedom from limitations in breaking down scenes made it 
imperative that it be possible to arrange the various planes in front 
of the camera in any order. That meant that the planes would have 
to be quickly and easily demountable from the structure and light 
enough in weight to be handled easily. It meant that each plane 



would have to carry its own light-boxes. Because of the large 
number of background separations desired, the overall height of the 
plane and light-boxes had to be kept to a minimum : it was possible 
to keep it under 14 inches. The contact planes had to carry all the 

FIG. 2. Multiplane camera, front elevation. 

usual cartoon facilities for handling animation, such as peg bars, 
platen, etc., in addition to the background support. 

The desire for controlling depth of focus over a large range made 
many revisions necessary in the usual cartoon camera set-up. Analy- 
sis of lenses of various focal lengths, focusing close to the camera, 
showed that the depth "of focus was practically independent of focal 
length for the same photographed field size. It remained for us to 
choose a lens with an angle that would give us a convenient range of 
field sizes within the limits of our structure. For a large enough 


depth of focus, it was necessary to stop the lens down as small as 
//32. In making three-color separation negatives, the small lens 
aperture raised the light requirements far in excess of those of the 
usual cartoon system. As we use stop-motion photography to make 
the successive color separations, we were able to reduce the light to 
about 500 foot-candles by increasing the exposure time. We es- 
tablished, for our purposes, exposure times varying from 0.9 to 9 
seconds per exposure. 

FIG. 3. Top view of camera carriage showing camera 
drive and "East- West, North-South" and rotational 

In mounting the camera, the usual small horizontal movements in 
two directions as well as the vertical movement were required. A 
rotational movement about the lens axis was also required for angle 
shots and airplane spin effects, etc. By a combination of horizontal 
and rotational movements, any type of angular or rotational move 
was possible. It was found necessary to equip each of the planes 
with a vertical truck movement, so that the photographed size of 
any scene element could be controlled individually. 

In lighting the photographed field, it was found feasible to paint 
for the effect desired and to use as flat a light as possible. However, 
provision was made for filters and special-effects masks over each 
light-box. The one most difficult problem was spill light. It was 
finally necessary to develop special light-boxes that would simul- 



taneously light the field flatly, have a high efficiency, keep spill light 
off the planes immediately above and below, and have an overall 
height limited to 10 inches. Heat from high-intensity light was 
serious and necessitated an exhaust system for all light-boxes (Fig. 2) . 
Because the operation of the machine was to be such that it could 
be tied into regular production, a planning group of technicians and 
artists had to be developed to prepare the necessary camera instruc- 

To minimize operation errors, an interlocked control system had 
to be developed that would keep the numerous machine adjust- 
ments coordinated. The regular 
cartoon system of scene set-up and 
exposure sheets had to be expanded 
to include the new elements and 
movements of the multiplane crane. 
The crane itself is a vertical four- 
post structure to which the various 
planes are movably attached. The 
four posts are rigidly held in rec- 
tangular top and base castings 40 
X 60 inches in size. The posts 
are unsupported except at the ends, 
and are ground steel tubes 4 7 / 8 inches 
outside diameter, with y 4 -inch walls, 
and are 11 feet 4 inches long. Each 
tube has a gear rack bolted on along 
its entire length. The rack teeth 
are matched so as to provide very 
accurate control of the height. In the control system, the optical 
axis and the floor form the origin. The rack teeth are numbered in 
inches, reading from the floor, to serve as height indicator for all 
equipment on the crane. The tubes are the guides and the gear 
racks are the supports for all the equipment. As can be seen from 
the general view of the crane (Fig. 1), the camera is at the top and 
photographs vertically down through the various planes. 

The camera carriage is a rigid platform guided by bushings and sup- 
ported by worm-driven rack gears (Fig. 3). The carriage is counter- 
weighted at each corner by weights hanging inside the tubes. On 
the camera carriage is an "east- west" dovetail slider which carries 
a "north-south" dovetail slider. On the north-south slider is a large 

FIG. 4. Service gutter for power 
feed to planes. 


ball-bearing ring which supports the camera and drive and allows them 
to rotate through an arc of 360 degrees. The camera is mounted so 
that the optical axis coincides with the center of rotation of the 
mount. Every movement has calibrations correlated to the pro- 
duction technic so that camera movements can be laid out and 
calculated, prior to photographing, with a high degree of accuracy, 
and, by the same means, any given set of conditions may be repeated 
at any time. Due to the requirement of variable exposure time, 
the camera is driven by a synchronous motor through a variable- 
speed transmission and stop-motion clutch. A selsyn motor is also 

FIG. 5. Adjusting reflectors with the special photometer. 

tied into the stop-motion shaft to drive the operation control mecha- 
nism and film counter. 

The most complicated of the scene element supports are the action 
levels or contact planes. The contact planes contain all the features 
of a standard cartoon photographing table, plus the background sup- 
port. The plane carries its own light-boxes. The power control 
circuits and compressed air are fed to the planes from a special 
gutter having a series of plugs and valves arranged along its length 
(Fig. 4). This gutter is mounted vertically and parallel to the rear 
left post of the crane. The background planes are fitted to carry 
transparent backgrounds of various widths in a movable east- west 
slide, each carrying its own light-boxes and control circuits. All 
the movements are fitted with calibrations referred to the optical 
axis as center, so that all planes have indications that are mutually 


FW. E. GARITY AND W. C. MCFADDEN [j. s. M. p. E. 


consistent. All planes are fitted with rack gear vertical supports 
and movements similar to those of the camera carriage. 

The lamp-boxes are of the adjustable facet reflector type, designed 
to fit a multitude of stringent conditions (Fig. 5). The reflectors are 
individually adjusted with the use of a caesium cell photometer de- 
signed especially for the purpose. The adjustments control flatness 
of the lighting as well as the intensity of illumination. 

Due to the fact that in the normal operation of this camera the 
services of one to six operators may be required, and their efforts 
must all be coordinated and the possibility of human error eliminated, 
all the indices have been provided with special illuminating lamps. 
While the operator of one plane is preparing his various controls for 
photography, these lamps permit him to read the indices. When 
he has set all the controls, he pushes a button, conveniently located 
on his particular plane, which turns out these lights, making it im- 
possible for him to read his control setting. When he pushes the 
button he trips a specially designed relay which cuts out the illumi- 
nation of his indices and places the electrical circuit in such condition 
that when all the planes have thus functioned, then and only then, can 
the chief operator trip the camera. These relays are connected by a 
series method so that all the relays from the various planes in opera- 
tion must be closed before the chief operator can energize the elec- 
trical mechanism that trips the camera. When the exposure is com- 
pleted to the chief operator's satisfaction, he pushes a button that 
releases all the planes simultaneously so that the individual opera- 
tors may proceed with establishing the settings for the next exposure. 

To correlate the detailed manipulation, it was found necessary to 
produce a master control sheet showing on it the settings of each 
plane for each successive operation. This master control sheet is 
made out in duplicate. The duplicate sheet is split up and the por- 
tion carrying the camera carriage instruction is given to the camera 
operator; the portion carrying the instruction covering plane A is 
given to the operator of plane A; and so on; and the original master 
is placed on a master control board immediately in front of the chief 
operator (Fig. 6). 

To eliminate errors on the part of the chief operator in knowing at 
just what frame he is working, a selsyn interlocked motor has been 
incorporated in the camera mechanism. A second selsyn motor is 
incorporated in the master control board and operates a glass ruler 
device that indicates to the chief operator exactly upon which frame 

154 W. E. GARITY AND W. C. MCFADDEN [J s. M. P. E. 

he is working. In other words, when a new control sheet is placed 
on the board, the glass ruler is returned to the first exposure, the 
interlocking motors are energized and the master ruler driven by 
the camera, regardless of whether the camera moves forward or 
backward. There is therefore no opportunity, except in the case of 
electrical failure, for the chief operator to make an error. 

In view of the fact that projection type lamps are used, and for 
the technicolor process it is required that they operate a voltage 
higher than rated, their lives are necessarily short. To circumvent 
this condition, an electrical circuit has been arranged to introduce a 
resistance into the main current supply line so as to reduce the volt- 
age on the lamps to about 85 or 90 volts during the time when changes 
and camera set-ups are being made. A special relay is provided in 
the circuit so that it is impossible for the chief operator to make an 
exposure while the protective resistance is in circuit. 

To increase the life of the bulbs further, as well as to reduce the 
heat in the camera area, it was necessary to incorporate an exhaust 
system in the lamp-boxes (Fig. 2) . This equipment was designed to 
provide one change of air per second in the lamp-box, and has been 
quite successful in increasing the useful life of the lamp besides pre- 
venting practically all heat conduction through the lamp-box. 

In the development and design of the light-sources used with the 
camera, it was necessary to develop special photometric equipment 
due to the acute angle of the light-source to the photographed area, 
which averages about 27 degrees. None of the commercial photo- 
metric devices was satisfactory. The device developed for this 
particular function contained a caesium photoelectric cell in a vac- 
uum-tube voltmeter circuit (Fig. 5) . The photocell was mounted so 
that its cathode scanned a small disk of heavy ground-glass suspended 
about 5 inches below the photocell. This glass disk is held in position 
by means of a piece of glass tubing about 2 inches long, the disk being 
centered at the bottom of the tube. The glass tube is suspended in 
a piece of brass tubing about 3 inches long, and the interior of the 
brass tube is entirely opaqued and rendered non-reflecting. 

The photocell and tube are suspended by means of a double 
trunnion of a design similar to that used to suspend a ship's compass. 
The outer pair of trunnions is established in a ring, and in the ring 
are set three posts so that the ground-glass disk is suspended about 
y 4 inch above the illuminated surface to be measured, and the three 
supporting legs are positioned so as not to cast a shadow upon the 


ground-glass disk. The instrument measures very accurately the 
perpendicular light, which is the useful photographic light. A de- 
vice of this type is necessary so that the reflection surface remain 
absolutely parallel at all times; a slight deviation from the level 
would cause a wide discrepancy in our measurements. This ap- 
paratus is useful only in leveling the overall illumination, and is 
impracticable for establishing the light levels for the photography. 
The scene-planning group of artists and technicians was developed 
to control the use of the multiplane crane in creating the desired 
illusions. In breaking down a scene the group works with a pencil 

FIG. 7. Multiplane set-up on crane showing four 
levels, with water and reflections. 

perspective layout of the scene as originally conceived by the layout 
department. After due allowance has been made for any special 
set-up for some particular effect, the scene is broken into its fore- 
ground, action, and background elements and these elements are 
indicated on the original layout (Fig. 7). As the original layout is 
already drawn to action-level size, every change in size for the sepa- 
rations is referred to the action level as a base. Field sizes are then 
chosen for each of the separated backgrounds and the separations 
are photostatically enlarged or reduced, depending upon their posi- 
tions above or below the action level. In order to get correct per- 
spective speeds in pan shots, the real-life distance from the action 
level to each separation is estimated by measuring the drawn size of 
similar objects in the original layout. The speed of motion for any 


plane is the contact-level speed multiplied by the ratio of the separa- 
tion-field size to the contact-level field size; and by the ratio of the 
drawn size of an object, in the original layout at the real-life dis- 
tance of the separation to the drawn size of the same object at the 
real-life distance of the contact level. 

To control the out-of -focus diffusion, a depth-of -focus chart is 
used. After a circle of confusion for a particular separation is 
chosen, and using the lens aperture that will give enough depth of 
focus, the field size of the separation can be set by using the dis- 
tance from the focal plane or contact level that will have the diffusion 
desired. In making finished backgrounds, photostats are traced 
upon the transparency to indicate to the artists the size and com- 
position. Then specially trained artists paint the elements. The 
artist must develop a high degree of skill to handle the color harmony 
from plane to plane in such a way that the planned effect of depth 
will be maintained. 

To lay out the master control sheets, the technicians keep records 
of all the decisions, as to the effects desired, upon a multiplane scene 
script. When the scene is completed for photography, it is checked 
for both artistry and mechanics, and then the master control sheets 
are laid out by the technicians who give the complete operating in- 
structions for each frame of film. 

The multiplane technic was first used and developed on the "Silly 
Symphony" entitled The Old Mill and was used extensively in the 
feature production Snow White and the Sewn Dwarfs. Following 
the latter, the Silly Symphony Wynken, Blynken and Nod was pro- 
duced in which the multiplane technic was also employed. The 
technic has definitely improved the photographic quality of the prod- 
uct and we are convinced that its possibilities are unlimited and 
that the results justify the increased cost of operation. 



Summary. When the spherical tip of an ideal reproducer stylus slides over a 
warped groove surface having a sinusoidal profile, the traced curve is not exactly 
sinusoidal. An analysis of the harmonic content of the traced curve, similar to that 
given by DiToro (J. Soc. Mot. Pict. Eng., Nov., 1937) but avoiding his approxima- 
tions, is directly applicable to reproduction from vertical-cut records. These results 
may be applied to reproduction from lateral-cut records by taking the original groove 
surface as inclined approximately 45 degrees from the horizontal, projecting the 
traced curve upon the horizontal and vertical planes, and adding in proper phase 
the guidance of the stylus tip by both sidewalk. It is shown that there is a residual 
vertical component of stylus motion ("pinch" effect) and complete cancellation of all 
even harmonics in the tracing distortion. Computation of the remaining odd har- 
monics indicates that, when the ideal lateral-cut reproducer characteristics include 
ideal "following" for vertical motion at signal frequency, a lateral-cut record may be 
reproduced with one-fourth to one-tenth the rms. distortion of a similarly recorded 
vertical-cut record. These results are displayed for convenient reference by contours 
of constant distortion upon a universal chart, the dimensionless coordinates of which 
characterize any recording condition and allow immediate specification of the 
maximum permissible recorded amplitude, maximum predistortion of the frequency 
characteristic, and the required clearance angle of the recording stylus . 

In the complicated process of recording and reproducing a phono- 
graph record there are many ways in which non-linear or harmonic 
distortion may enter the system. If one assumes that the electro- 
mechanical conversion is perfect in both recording and reproduction 
there still remain two geometric factors introducing harmonic dis- 
tortion which may not be reduced except by altering the dimensions 
of the apparatus. The first of these is "tracking error," and may be 
defined as the angle between the vertical plane containing the vibra- 
tion axis of the mechanical system of the reproducer and a vertical 
plane containing the tangent to the record groove. Such an angle 
arises from the convenient mechanical device of pivoting the re- 
producer tone-arm from a fixed point. If the vibration axis of the 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 15, 1938. Published also in /. Acoust. Soc. Amer. (July, 1938). 
** Cruft Laboratory, Harvard University, Cambridge, Mass. 


158 J. A. PIERCE AND F. V. HUNT [j. s M. P. E. 

reproducer, extended, passes through the tone-arm pivot, it may 
readily be shown that the vibration axis can never be truly tangent 
to the record groove at more than one value of the radius. On the 
other hand, if the vibration axis of the reproducer system is set at an 
appropriate angle with the line connecting the stylus tip and the tone- 
arm pivot, and if the length of the tone-arm is properly adjusted to 
the distance between the tone-arm pivot and the record axis, then 
the tracking error may be held to a few degrees. In the case of re- 
production of vertical-cut records this tracking error does not intro- 
duce distortion and the tone-arm may therefore be made quite short. 
On the other hand, in the reproduction of lateral-cut records a sinus- 
oidal groove is not traced sinusoidally by the reproducer stylus tip 
if the tracking error is considerable. Olney 1 has discussed this effect 
and has given numerical examples of the harmonic distortion intro- 
duced under practical recording conditions. He shows, for example, 
that even with so large a tracking error as 15 degrees (as large as is 
usually met in practice) the maximum distortion to be expected from 
this source is approximately 4 per cent. On the other hand, it is 
readily possible to offset the vibration axis in such a manner that the 
tracking error does not exceed 6 degrees, and under these condi- 
tions the harmonic distortion introduced by tracking error can be 
neglected in comparison with other distortions met with in a practical 
recording system. 

A very much more serious source of harmonic distortion arises 
from the fact that the tip of the reproducer stylus has finite size. 
The curve traced by the center of the tip (which we shall assume to 
be spherical) of a reproducer stylus sliding over a sinusoidal groove 
surface is not, unfortunately, sinusoidal, and it is embarrassing that 
the only way to reduce the distortion due to this effect is to reduce the 
size of the needle tip. Such reduction can be carried only so far, 
with the practical result that this distortion, herein called tracing 
distortion, currently remains the most serious limitation in the at- 
tainable fidelity of phonograph reproduction. DiToro 2 has dis- 
cussed this type of distortion with an analysis based upon an approxi- 
mate sine curve composed of parabolic and straight-line sections, and 
has given results that are applicable to reproduction from vertical- 
cut records. These results are satisfactory for high values of dis- 
tortion, but are in some error at the lower and more interesting values. 
It is the purpose of this paper to present an extension of this work, 
based upon a method of computation that avoids DiToro's approxi- 


mations, and to apply the results to an evaluation of the tracing dis- 
tortion arising in the reproduction of both vertical and lateral-cut 


The first step in the solution of this problem lies in the harmonic 
analysis of the curve traced by the center of a circle that slides or 
rolls along a sine curve. These results will give directly the com- 
ponents of motion of a spherical needle tip tracing a vertically 
modulated record groove, and the application of the results to the 
analogous motion of a needle tip tracing a laterally modulated groove 
will be discussed later. Fig. 1 represents such a circle sliding along 
a cosine curve. It will be noted that the traced curve (shown dotted) 
is not mathematically simple. It is, however, so simple physically 
that it seems as though it should be numbered among the curves that 
are dignified by titles, and for want of a better name we have 
dubbed this curve the poid and shall so designate it in this discussion. 

The coordinates of the center of the tracing circle, , 77 (which are 
the coordinates of a point on the poid), may be expressed in terms of 
the corresponding coordinates of the point of contact of the circle 
with the cosine curve, as follows: Let axes be established as indi- 
cated in Fig. 1 so that the cosine curve is defined by 


y = a cos - = a cos kx (1) 



k = 27T/X 


= x + r sin 

but, tan 8 is the slope of the cosine curve at the point (x, y), or 

tan = ka sin kx 

ka sin kx 

sm = 


VI + k*a* sin* kx 

77 = y + r cos 
= a cos kx + -7====L=== (5) 

160 J. A. PIERCE AND F. V. HUNT [j. s. M. p. E. 

These parametric equations for the poid have involved no approxi- 
mations. Unfortunately the elimination of x between them and the 
expansion of 17 in a Fourier series in is extremely difficult, each coef- 
ficient involving the term-by-term integration of the product of 
three infinite series, none of which converges rapidly for the range of 
values in which we are interested. 

An alternative method of solution was therefore sought. Chaffee 3 
has described a simplified form of schedule analysis, applicable to 
even functions, which is capable of considerable accuracy and re- 
quires a knowledge of the coordinates of only a limited number of 
points. The poid is an even function, as indicated by its symmetry 
about either a maximum or a minimum point, so that, with the co- 
ordinates of only seven points in a half -wavelength, the amplitudes 
of the second and third harmonics may be determined within one or 
two per cent, and reasonably accurate values may be calculated for 
harmonics up to the sixth. This precision was deemed adequate for 
our purpose. 

It was required, then, to determine values of t] corresponding to 
the values of k prescribed by the harmonic analysis schedule. The 
values of x corresponding to these prescribed values of k were first 
obtained by successive approximations, assumed values of x being 
inserted in equation 2 until k% was established with sufficient ac- 
curacy. These values of x for each prescribed point were successively 
inserted in equation 3 and the resulting values of ?j used to enter the 
harmonic analysis schedule. The relative amplitudes of the six 
harmonics were then obtained by simple arithmetic. 

This method of computation, while laborious, requires no ap- 
proximations except those inherent in the schedule analysis and these 
may be made as small as desired by computing a sufficiently large 
number of points. By making check calculations using as many as 
thirteen points for a half -cycle it was found that the "seven -point" 
analysis was indeed sufficiently accurate. 

On reference to Fig. 1 it may be noted that the size and shape of 
the poid, and therefore the amplitude of each harmonic constituent 
of the poid, is given by three linear dimensions, a, r, and X. On the 
other hand, the shape of the poid and the relative amplitudes of its 
harmonic constituents are determined by the two dimensionless 
ratios, a/\ and r/X. Our subsequent discussion will be simplified 
if we take these ratios as 2ira/\ and 2irr/\ (i. e., as ka and kr), and we 
may then say that the relative harmonic structure of the poid is a 


function of the two independent variables ka and kr. It is necessary 
now only to calculate the distortion corresponding to all possible 
values of these two variables a straightforward but tedious process. 

The values of harmonic distortion so calculated might be plotted 
vertically over the ka-kr plane and constitute a characteristic surface 
whose distance above the horizontal plane is a measure of the har- 
monic distortion for the condition corresponding to the coordinates 
ka and kr. It is frequently convenient to represent such a warped 
surface by projecting onto the horizontal ka-kr plane contours of 
selected constant values of harmonic distortion. It is thus possible 
to represent on a single chart the entire range of tracing distortion 
met under all recording conditions. The computational labor in- 
volved in obtaining such a set of contours is reduced by the prepara- 
tion of a family of intermediate curves, each showing harmonic dis- 
tortion plotted against the variable kr with selected values of ka held 
constant for each of the intermediate curves. If horizontal lines are 
now drawn at the chosen values of the total harmonic distortion, they 
will cut the family of intermediate curves in a series of points which 
establish the pairs of coordinates for the points lying along the con- 
stant-distortion contour curve. These points are then transferred to 
the ka-kr plane and the contours drawn as exhibited by the dashed 
lines of Fig. 4. By this method the harmonic analysis of some thirty 
poids is sufficient to establish the contour set covering the entire 
useful range of the independent variables ka and kr. 

It may be pointed out that the harmonic analysis schedule yields 
the amplitudes of the various harmonics. Inasmuch as reproducing 
systems are almost invariably velocity-responsive (either intrinsically, 
as in the electromagnetic, or through equalization, as in the piezo- 
electric) each harmonic amplitude is multiplied by its harmonic 
number before comparison with the amplitude of the fundamental, 
and the contour chart of Fig. 4 is then drawn in terms of the total 
root-mean-square harmonic velocity distortion.* 

As suggested above, the dashed-line contours of Fig. 4 are directly 
applicable to reproduction from vertical-cut records, and their in- 
terpretation under specific recording conditions will be given in a 
later section. Before applying these results to the reproduction of 

* If v\ t i>2, Vs, are the harmonic velocity components the total rms. distor- 
tion is defined as 


162 J. A. PIERCE AND F. V. HUNT [j. s. M. p. E. 

lateral-cut records we must consider in greater detail the geometrical 
relation between a laterally modulated groove and the stylus tip. 
Fig. 2 is a plan view and two typical cross-sections of a laterally 
modulated record groove. This groove is generated by a plane cut- 
ting surface which is always perpendicular to the axis of the un- 
modulated groove. There arises, consequently, a constriction in 
the width of the groove, measured perpendicular to its instantaneous 
direction, whenever the cutting needle is moving at an angle to the 
direction of the unmodulated groove. This is illustrated by the 
sectional views of the groove given at the bottom of Fig. 2. If such 
a groove be traced by a stylus that bears at least partially upon the 
groove sidewalls, it will be seen at once that the stylus must rise and 
fall twice during the tracing of each fundamental wavelength. This 
phenomenon appears to have been ignored or neglected in previous 
discussions of the so-called "pinch effect," but it leads to the neces- 
sary conclusion that an ideal reproducer for lateral-cut records must 
embody sufficient vertical flexibility to enable the stylus to execute this 
motion faithfully. This requirement appears even more severe when 
it is remembered that this vertical motion must be executed at twice 
the frequency of the fundamental groove modulation. In typical 
commercial reproducers for lateral-cut records there is no provision 
for vertical motion of the stylus relative to the tone-arm, with the 
result that the stylus must ride at some intermediate elevation above 
its normal position in the unmodulated groove. Since the mass of 
the reproducer head and arm is too large to be vibrated at signal 
frequencies, the stylus is driven into the groove in the "pinched" 
sections. This gouges out the groove walls, producing additional 
surface noise and altering the original groove shape. When the 
groove section is not "pinched" the stylus floats above the groove 
and is free to "rattle" since it is not necessarily in contact with either 
wall. With conventional reproducing apparatus this process con- 
tinues until the pinched sections of the groove have been enlarged 
(involving the erasure of any small amplitude high-frequency modu- 
lation that may be superimposed), or the needle has been worn. 
The needle tip then rides at some constant level but is never there- 
after positively driven by more than one groove wall at a time. 
Olney 1 has pointed out that distortions may arise from this con- 
dition. On the other hand, if the stylus point is sufficiently sharp to 
reach the rounded bottom of the "standard groove" the result is 
equally bad; while the tendency to vertical motion is minimized or 



FIG. 1. Coordinates and nomenclature for the harmonic analy- 
sis of the curve ("poid") traced by the center of a circle sliding or 
rolling along a cosine curve. 



FIG. 2. Plan and sectional views of the assumed stylus bearing 
relations in a typical laterally modulated groove. 



[J. S. M. P. E. 

removed, the stylus is never positively driven by the groove. It is 
not possible to make an accurate quantitative analysis of the dis- 
tortion introduced by the uncontrolled rattling of a stylus tip in a 
record groove, but it seems reasonable to assume that the distortion 
under such conditions will be at least as large as would be generated 
if the stylus were in continuous contact with the groove walls. More- 

FIG. 3. Section and projected plan 
views illustrating the stylus displacement 
components during the tracing of a later- 
ally modulated record groove. 

over, the distortion generated by rattling would be inharmonic, and 
as this would contribute noise as well as signal distortion, we may con- 
dude that an ideal reproducer whose stylus is positively driven by the 
groove walls will yield a lower background noise level. 

It seems, therefore, that it is highly desirable in practice, and neces- 
sary for a mathematical analysis, to endow our assumed ideal lateral 
reproducer with such characteristics that it can execute the pre- 
scribed vertical motion faithfully, and we further assume and hold 


as desirable that the stylus should be supported by the sidewalls of 
the groove. With a spherical stylus tip this does not lead to a large 
increase in needle bearing pressure in practice, and we assume here 
and throughout this discussion that no account need be taken of the 
distortion of the groove surface by the needle bearing pressure. 
When these conditions are satisfied we may discuss the components 
of stylus motion with the assistance of Fig. 3. 

Consider that BC and B'C' are the projections onto the plane of 
the paper of the two extreme positions of a radial section of one wall 
of a groove that is modulated laterally with an amplitude a. As the 
record rotates, this groove wall is generated as a wavy surface having a 
sinusoidal profile. The curve traced by the center of a ball sliding 
upon this surface, if projected upon a plane perpendicular to BC, as 
indicated by DG, will be a poid which will have a maximum and a 
minimum at G and F, respectively. In this plane through DG, per- 
pendicular to the paper, the amplitude of the sine wave is a sin a, 
and the poid may be represented by 

17' == a\ sin a cos k% + a-2 sin a cos 2k% + #3 sin a. cos 3k!; + . . . (6) 

This poid may be projected upon a plane parallel to AB, such as the 
one through HJ, by dividing equation 6 by 

cos (x/2 2a) = sin 2a = 2 sin a cos a 
Its equation now becomes, 

cos * + cos 2** + =-- cos 3k* + . (7) 

2 cos a ' 2 cos a '2 COS a 

This equation expresses the motion of the sphere caused by the 
change in position of the sidewall represented by BC and B'C', and 
since the motion is projected upon a plane parallel to the opposite 
sidewall it may be divided into components, in both the vertical and 
horizontal planes, which are independent of any simultaneous mo- 
tions of the opposite sidewall. For example, the horizontal com- 
ponent of the motion is given by 

n' H = |cos^ + | 2 cos2^ + | cos 3** + ... (<?) 

The corresponding equation for the component of motion induced 
by the opposite sidewall is identical except for direction and a phase 
difference between the two poids. It is to be noted that there is a 
phase displacement of 180 degrees in the equation of the motion due 
to the sidewall indicated by AB; that is, the maximum of one poid 

166 J. A. PIERCE AND F. V. HUNT [j. s. M. p. E. 

occurs simultaneously with the minimum of the other. This is in- 
dicated by the plan view, shown in the upper part of Fig. 3, which 
represents the projection onto the horizontal plane of the sine curve 
profile of the groove walls and the poids generated in the planes 
through HJ and HJ'. The horizontal projection of the poid gener- 
ated by the wall AB is directed oppositely to that generated by the 
wall BC, as viewed, say, from the center of the record, because the 
sphere is being pushed away from the center of the record in one case 
and toward it in the other. The expression for the horizontal com- 
ponents of motion generated by the second poid is given, therefore, 


,' H = - I' COS (TT + *{) - | COS 2(ir + ftf) - |' COS 3(7r + *{) - . . . 
= | cos * - | cos 2k + I cos 3*{ - . . . (9) 

As shown by the directed arrows in Fig. 3, when the displacement of 
the groove is away from the center of the record the stylus is forced 
to move part way in this direction by the displacement of the inner 
groove wall, and allowed to slide the remainder of the way by the 
retreat of the other wall. 

The total lateral motion of the stylus is, therefore, the sum of 
the motions induced by both sidewalls, or 

T; H = a\ cos k + o 3 cos 3k -f- . . . (10) 

This yields at once the important result that the even harmonics of 
the fundamental frequency are cancelled out of the lateral motion 
of the reproducer stylus. Returning to equation 7 and projecting 
the poid on the vertical plane through H by multiplying the equation 
by sin a, we find for the component of vertical motion induced by the 
sidewall BC, 

. a\ tan a . . a?, tan a _. , . . 0,3 tan a _ , / - - \ 
TI' = - L ~ - cos k + ==- - cos 2k + cos 3k + . . . (11) 

For the component of motion induced by the opposite sidewall we 
have still the 180-degree displacement in phase, but the direction of 
the displacement represented by the poid is in this case the same, 
that is, upward. Hence, for the wall AB, 

a\ tan a , . , fcN , a 2 tan a n , 
il'y = g cos ^ + k ^ 2 S ^ + 

cos 3(,r 


.. (M) 

As before, the resultant vertical motion is given by the sum of the 
components of motion induced by the two sidewalls and is 

i) v = a z tan a cos 2k + . . . (13) 

We may, therefore, extend the conclusion stated above as follows: 
the lateral motion of a stylus tracing the groove of a lateral-cut record is 
determined by the fundamental and odd harmonics only of the poid 
characterized by the groove amplitude, the wavelength, and the needle 
radius; the even harmonics of the poid appear as vertical motion and 
constitute the "pinch" effect. 

It may be pointed out for contrast that in the corresponding case 
of a vertical-cut record the motion of the two sidewalls is in phase, 
the maxima of the two poids occur simultaneously, the lateral mo- 
tion is completely cancelled out, and all the harmonic constituents of 
the poid enter into the expression for the total vertical motion. 

The difference in the distortions arising in the reproduction of 
these two types of groove modulation is emphasized by the observa- 
tion that positive drive of the stylus tip by both sidewalls of the groove 
yields the usual advantages of a push-pull system, with the result 
that a large part of the distortion inherent in the reproduction of vertical- 
cut records is entirely absent in the reproduction of lateral-cut records 
when a satisfactory lateral reproducer is employed. The latter qualifi- 
cation is added to indicate that the specifications of the ideal lateral 
reproducer here assumed are somewhat unconventional, and these 
reduced distortion levels are not to be expected generally with the 
present types of conventional lateral reproducers. 

On this basis we may return to the original data upon which the 
dashed contours of Fig. 4 were based and compute the root-mean- 
square value of the odd harmonics, prepare a set of intermediate 
curves, and establish the solid-line contours as characteristic of the 
distortion generated in the reproduction of a lateral-cut record. 


We turn now to a more detailed discussion of the chart upon which 
contours of constant distortion are represented. A choice of loga- 
rithmic scales for the two coordinate axes endows the contour 
chart with the interesting property that almost all the characteristic 
quantities, in terms of which the performance of a phonograph system 

168 J. A. PIERCE AND F. V. HUNT [j. s. M. p. E. 

is analyzed, are represented on the chart by straight lines which are 
horizontal, vertical, or inclined at 45 degrees to the principal axes. 

(A) The ordinate scale, ka, gives directly the ratio of the maxi- 
mum cyclic stylus velocity to the tangential groove velocity, so that, 
other factors being held constant, a vertical line on the chart repre- 
sents a change in the recorded velocity amplitude. Since the or- 
dinate scale is logarithmic, a uniform scale, as appended to the right- 
hand margin of the chart, may yield the velocity amplitude in deci- 
bels referred to the tangential groove velocity as zero level. Such 
a scale is convenient for estimating changes in the recorded level. 

The maximum radial velocity of the stylus occurs as the center-line 
of the groove crosses the line of the unmodulated groove, and the 
cutting angle is therefore a maximum at that time. The tangent of 
this angle is given directly by ka so that a subsidiary scale may be 
appended to the upper right-hand corner of the contour chart es- 
tablishing the minimum value of the clearance angle of the cutting 
stylus required in order that the groove be cut without interference 
from the trailing edge. 

(B) A 45-degree line on the contour chart extending from the 
lower left to the upper right is a line corresponding to a constant ratio 
of the amplitude of groove modulation to the stylus tip radius. 
Along such a sloping line, drawn for a given ratio, a/r, one may plot 
frequency increasing upward to the right or tangential groove ve- 
locity increasing downward to the left, according as one or the other 
variable is assumed constant. 

(C) As indicated under A, a horizontal line on the contour chart 
is a line of constant velocity amplitude. Inasmuch as this represents 
the usual ideal recording situation it represents an important locus, 
and, in general, frequency increases toward the right along such a 
horizontal line. There will always be, for any assumed standard 
conditions of record speed, maximum amplitude, and stylus radius, 
some record radius for which a horizontal line would allow frequency 
to be read directly from the scale of abscissa, in kilocycles. This 
record radius is frequently an unusable one, but the reference line so 
denned is convenient in that a frequency may be located on this line 
and a projection made along a 45-degree line downward to the left 
to the record radius desired. 

(D) A 45-degree line extending from the lower right to the upper 
left is a line for which the product of ka and kr is constant. It can be 
shown that along such a line the ratio of the radius of the needle tip 


to the minimum radius of curvature of the record groove is constant. 
For example, a line having this slope and passing through the (1,1) 
point is the line for which the ratio of these curvatures is unity. All 
traced curves represented by points lying above and to the right of 
this line are poids having a cusp. 


One striking characteristic of the constant-distortion contours 
exhibited in Fig. 4 is the fact that, except in the upper portion cor- 
responding to extreme values of velocity amplitude, the contours 
are straight lines inclined at 45 degrees to the principal axes. So far 
as this is an accurate description of the contours, we may derive cer- 
tain general relationships by examining the distortion as this family 
of 45-degree lines is cut by other lines representing loci of constant 
parameters of the recording conditions. 

(1) As suggested above under D, a 45-degree line having the orien- 
tation of the contours is a line along which the ratio of the needle tip 
radius to the minimum radius of groove curvature is constant. Ex- 
amination of the contours indicates that for vertical reproduction 
the total distortion varies linearly with the ratio of these radii. For 
lateral reproduction the total distortion is smaller and varies as the 
square of this ratio. It may be pointed out that if the frequency, the 
groove speed, and the needle tip radius are constant, then the ratio 
of the groove and needle tip curvatures, and hence the total distortion 
for vertical reproduction, is a linear function of the recorded ampli- 
tude. For lateral reproduction the corresponding total distortion is 
proportional to the square of the recorded amplitude. The ratio of 
the radii of curvature has frequently been offered as a criterion of the 
upper limit of frequency that could be reproduced satisfactorily. 
Our study indicates that this is indeed a satisfactory rough criterion 
of distortion, and it may be seen from the chart that equality in these 
radii corresponds to approximately 40 per cent total distortion for 
vertical reproduction and 20 per cent total distortion for lateral re- 
production. If one selects 10 per cent total distortion as a tolerable 
limit, the required ratios are approximately 3 / 6 for lateral and 1 / 6 for 

The velocity amplitude of any harmonic component, relative to 
the fundamental component, may be determined by the simple em- 
pirical relationship, 

(kakr} n ~ l 
H n = (KaKT) (14} 



[J. S. M. p. E. 






I 50 " 






FIG. 4. Universal chart, for velocity-responsive systems, dis- 
playing contours of constant rms. total harmonic distortion, for 
both vertical- and lateral-cut records, plotted against the di- 
mensionless independent variables ka and kr. 



1 1 




FIG. 5. Recording loci superimposed upon the ka-kr chart. 
Along the heavy reference line for V = 4?r in. /sec. the frequency 
may be read directly in kilocycles from the abscissa scale. 


where n is the number of the harmonic. Comparison of this relation 
with the preceding approximate statements about the variation of 
the total harmonic distortion confirms the fact that the principal 
component of distortion for vertical reproduction is a second har- 
monic, while the principal distortion component for lateral reproduc- 
tion is a third harmonic. 

(2) A horizontal line, as discussed under C above, is a line of con- 
stant velocity amplitude, along which frequency increases toward 
the right. Examination of the chart reveals that total distortion 
varies directly with the frequency for vertical reproduction and as 
the square of the frequency for lateral reproduction. On the other 
hand, if the frequency and other reproducing conditions remain con- 
stant, then points corresponding to a variation in needle tip radius 
will lie along the horizontal line, and the total distortion will increase 
linearly with the needle tip radius for vertical and as the square of 
the needle tip radius for lateral. 

(3) If both the recorded velocity amplitude and the needle tip 
radius be held constant as either the record radius or the record speed 
is varied, the values of both ka and kr change simultaneously, so that 
the contour curves are crossed along a 45-degree line extending from 
lower left to upper right. Examination of the chart then indicates 
that, for vertical reproduction, the total distortion varies inversely 
as the square of either the record radius or the record speed, accord- 
ing as one or the other of the two variables is held constant. For 
lateral reproduction the total distortion increases inversely as the 
record radius or record speed raised to the fourth power. 

Summarizing these approximate relations, we may say that in 
general the distortion obtained in lateral reproduction is always lower 
than in vertical but that it varies more rapidly with the parameter 
introducing the distortion. Two additional characteristics of the 
contour chart may be pointed out in this connection. The total dis- 
tortion for either lateral or vertical shows a distinct "saturation" as 
the distortion approaches some high value. In the case of lateral 
this saturation value is approximately 48 per cent; for vertical the 
saturation value is nearly 80 per cent. It will be noted that no con- 
tours have been drawn on the chart indicating the reduction in the 
amplitude of the fundamental component as the distortion increases. 
This omission was made in the interests of avoiding confusion in the 
contour chart. The data indicate that the contour lines correspond- 
ing to 20 per cent distortion for lateral or 40 per cent distortion for 

172 J. A. PIERCE AND F. V. HUNT [j. s. M. P. E. 

vertical correspond roughly to a reduction in fundamental amplitude 
of approximately 0.7 db. in either case. It is obvious therefore that 
the total harmonic distortion will have reached intolerable propor- 
tions before there is any significant reduction in fundamental ampli- 
tude. It follows that an appreciable "quality" difference between 
the inside and outside radii of a recording, detectable as a loss in high 
frequencies, must inevitably be accompanied by a serious increase in 
harmonic distortion and should never be tolerated in a high-fidelity 
system. The provision of variable equalization for recording at the 
inside of a record , which has been seriously proposed, appears to be 
defensible only as a partial corrective for the characteristics of a re- 
corder that relies principally upon the recording medium for damping. 


We shall now illustrate the application of the contour chart to an 
evaluation of the distortion arising under typical recording condi- 
tions. We shall assume for this purpose that the record is cut with 
100 grooves per inch, each groove being 6 mils wide at the surface of 
the record, 2.5 mils deep, with an included angle of 90 degrees, and 
having a bottom surface rounded to a radius of curvature of approxi- 
mately 1.25 mils. Under these conditions the assumptions regarding 
support of the stylus tip by the sidewalls of the groove may be satis- 
fied by a stylus having a tip radius of 2 mils. The maximum al- 
lowable amplitude of modulation, determined by the groove spacing, 
will also be 2 mils. If the record is vertical-cut, only the assumed 
values of a and r are material. For the standard recording condi- 
tions we shall assume that the amplitude of the cut is constant for 
frequencies up to 300 cycles, and that the velocity amplitude is main- 
tained constant at all higher frequencies. The constant-amplitude 
portion of this recording locus is represented by the left-hand margin 
of the parallelogram superimposed upon a ka-kr chart in Fig. 5. 
Frequency increases upward along the left-hand border of the paral- 
lelogram, and the frequency 300 cycles, at which the recording locus 
breaks into a horizontal line, occurs at some point dependent upon 
the tangential groove velocity. Four such horizontal lines are il- 
lustrated, corresponding to the inside and outside radii of typical 
33 and 78 rpm. recordings. For the assumed stylus tip radius the 
reference line along which frequency may be read directly from the 
scale of abscissas occurs at a groove velocity of 4ir inches per second. 
A 45-degree system of projection coordinates is based upon this ref- 

Aug., 1938] 



erence line and allows any frequency, established along the reference 
line, to be referred to the appropriate record radius. For example, if 
it is desired to determine the distortion at 5000 cycles, 2-inch radius, 
78 rpm., the procedure is as follows: follow the ordinate kr = 5 
upward to the standard reference line, trace downward along the 45- 
degree line to its intersection with the horizontal corresponding to 
78 rpm., 2-inch radius, interpolate between the contours to determine 


ORD 1 




33 '/3 R.P.M. 




/ y 






y ' 





AMPLITUDE - 0.002" 















R = 


| < 










- ' 




100 200 

500 1000 2000 5000 10000 20000 


FIG. 6. Total distortion plotted as a function of frequency for con- 
stant velocity amplitude and typical recording conditions. 

the total (lateral) harmonic distortion as 22 per cent. Following 
this procedure we may derive the data exhibited in Fig. 6, showing the 
rms. total distortion at typical inside and outside radii for 33- and 
78-rpm. recordings, both lateral- and vertical-cut. These curves 
exhibit clearly the marked superiority of lateral-cut over vertical-cut 
with regard to distortion, and indicate also the more rapid increase in 
distortion for lateral-cut as the frequency increases. One may be 
pardoned for wondering, on examination of the curves of Fig. 6, how 
it can be that records sound as well as they do in view of these serious 



fj. S. M. P. E. 

distortions. The explanation of this anomaly lies in the fact that 
speech and music by no means present the recording medium with 
the necessity of recording a constant velocity amplitude at all fre- 
quencies. The valuable data of Sivian, Dunn, and White 4 on the 
intensity distributions in speech and music are available for an eval- 
uation of this situation. We present our interpretation of these data 
in Fig. 7 in order to avoid any ambiguity about the application of 
this correction. The two curves for speech and music are arbitrarily 
shifted vertically to have the same peak amplitude inasmuch as an 
adequate volume indicator should indicate these peaks and provide 
a common basis for level control. The manner of applying these 
correction data to the distortion contours consists in locating fre- 



MUSIC, ^y/ 










'Y / 






/ /^-SPEE 











ICO 300 1000 3000 


FIG. 7. Peak power as a function of frequency (from the data 
of Sivian, Dunn, and White) used to evaluate the distortion in re- 
corded speech or music. 

quencies along the broken-straight-line recording locus as before, 
but interpolating between the contours for a point shifted vertically 
downward by the number of decibels plotted for the corresponding 
frequency in Fig. 7. These corrected values of distortion might be 
shown along with the curves of Fig. 6 for constant velocity ampli- 
tude, but for the illustration of an alternative method of exhibiting 
these data, we have prepared the curves of Fig. 8. These show the 
minimum value of record radius that will allow the music spectrum 
of Fig. 7 to be recorded with a total distortion not exceeding 10 per 
cent, plotted as a function of the frequency. The corresponding 
correction for speech would yield similar curves but without further 
rise beyond 2500 cycles. The nearly horizontal portions of the 
curves of Fig. 8 indicate that the present accepted standard inside 
radii for lateral-cut transcription and commercial pressings are ac- 


ceptable for the satisfaction of the 10-per cent distortion limit, but 
that, for the assumed amplitude of groove modulation, the 33-rpm. 
vertical transcription record is not capable of meeting the 10-per cent 
distortion specification without a reduction in needle tip radius. 


In connection with his study of vertical reproduction, DiToro 2 
has measured the relative amplitude of the second harmonic for values 
of ka and kr lying in the lower right-hand corner of our contour dia- 
gram. The agreement between his experimental observations and 
our calculations is quite good for this type of measurement, and may 
be considered adequate to confirm the dotted contours of Fig. 4. 

In view of the significantly lower distortion revealed by this study 
to be characteristic of lateral reproduction, it seems worth while to 
present some experimental data confirming these predictions. A 
direct-reading distortion meter operating at 400 cycles was used, and 
in order to simulate the conditions that would occur at a higher fre- 
quency at normal groove velocities, records were made and played 
back at speeds of 9 and 13 rpm. By thus shortening the wavelength, 
values of ka as high as 0.7 were obtained with kr no greater than 2, so 
that we were able to investigate the most useful part of the ka-kr 
diagram. A new type of lateral reproducer 5 satisfying the conditions 
assumed in the distortion analysis was employed. 

The test grooves were cut on lacquer-coated records. The cutting 
head used relies to some extent upon the record material for damping 
and so did not yield a constant amplitude at all groove speeds. This 
was taken into account in constructing the solid "calculated" curves 
of Fig. 9, the larger amplitudes being measured optically while the 
smaller were found by measuring the relative reproducer outputs at 
the fundamental frequency. Measurements were made at various 
record radii for two record speeds and for three different recording 
levels. The results are shown in Fig. 9 and seem to provide a wholly 
satisfactory verification of the mathematical analysis. 

The residual distortion levels of 2, 5, and 10 per cent, shown at the 
right-hand side of Fig. 9, may be attributed to the recording equip- 
ment, and principally to the recording head itself. It is, however, 
obvious that for the smaller values of tangential groove velocity 
tracing distortion is the predominant factor, and that its magnitude 
has the calculated value. It may also be concluded that not only 
were the reproducer specifications satisfactorily met, but that the 



[J. S. M. p. E. 

1000 . 3000 


FIG. 8. Distortion data for the music spectrum (solid lines), ex- 
hibited by plotting the minimum groove radius for which the dis- 
tortion will never exceed 10 per cent. The dashed curves corre- 
spond to constant recorded velocity amplitude. 


FIG. 9. Experimental data verifying the calculated distortion for 
lateral reproduction. 


assumption made in the analysis regarding the negligibility of mo- 
mentary deformations of the groove sidewalls was justified. 


A method of reducing the effective surface noise level has been sug- 
gested, and in some cases utilized, that consists in predistorting the 
recording frequency characteristic in such a way that high-frequency 
components are recorded at an increased level. Complementary 
equalization in the reproducing system restores the original balance 
and at the same time suppresses a portion of the surface noise gener- 
ated in reproduction. The distortion contour chart provides a 
method of evaluating the effect upon harmonic distortion of this type 
of alteration of the frequency response of the recording system. We 
have indicated above that in vertical -cut records the total distortion 
is a linear function of the recorded amplitude so that it would appear 
at first sight that it would be permissible to enhance the high fre- 
quencies in recording, allowing the distortion to increase linearly, 
and in the complementary equalization not only restore the original 
tonal balance but also return the relative harmonic distortion to the 
original value it would have had without modification. This is in- 
deed a useful method of reducing effective surface noise so long as its 
use does not increase the distortion beyond the range for which the 
second harmonic, which is the component varying linearly with am- 
plitude, is the principal distortion factor. If significant distortion 
terms higher than the second occur, not only will they increase more 
rapidly, and hence not be proportionately removed by the reproduc- 
ing equalization, but the higher terms will also contribute cross- 
modulation products which would not have been present at the 
original distortion level. Inasmuch as the distortion level is already 
high for vertical reproduction under typical conditions of groove 
amplitude and stylus radius, it appears that the gain to be derived 
from a predistorting technic is rather limited. On the other hand, in 
the case of lateral groove modulation, the total distortion increases 
with the square of the recorded amplitude, so that an increase in 
distortion introduced by modification of the recording frequency 
characteristic would not be compensated by complementary equali- 
zation in the reproducing system. It appears, therefore, that in this 
case the predistorting technic can never be employed unless the needle 
tip radius can be reduced to such an extent that tracing distortion is 
a negligible factor in the overall distortion of the system. 

178 J. A. PIERCE AND F. V. HUNT [j. s. M. p. E. 

The effect of cross-modulation mentioned above should be em- 
phasized in connection with the curves of Figs. 6 and 8. It is probable 
that we are seldom if ever interested in the harmonic distortion com- 
ponents accompanying fundamental frequencies higher than 4000 
to 6000 cycles. On the other hand, the cross-modulation products 
that accompany such distortion are of considerable interest, and, al- 
though difficult to analyze accurately, are approximately of the same 
magnitude as the harmonic components themselves. Thus, all the 
distortion data presented above for frequencies higher than about 
5000 cycles are to be interpreted as indicative of the magnitude of 
the cross-modulation components. These components are observed 
aurally in wide-range systems as a "burr" accompanying loud pas- 
sages. The sum and difference tones, being inharmonic, are more 
objectionable than comparable harmonic overtones. Thus, even 
though the overtones of these high frequencies may be outside the 
transmission band of the reproducing channel, the distortion limits 
that should be imposed upon a high-fidelity system are more severe 
than for the lower frequencies. These considerations indicate that 
the 10-per cent distortion limit assumed for the curves of Fig. 8 is 
too high to be acceptable if the overall system response is to extend 
significantly above 5000 cycles. 

A second conclusion can be drawn from the foregoing exhibition 
of the distortion performance of typical vertical and lateral recording 
conditions, based upon the broken-straight-line envelope of the peak- 
power correction curve shown in Fig. 7. It may be seen from this 
curve that the low-frequency peak amplitude falls off by slightly 
more than 6 db. per octave for frequencies below 250. On the other 
hand, this is exactly the reduction in velocity amplitude that one 
seeks to gain by altering the standard cut from constant velocity to 
constant amplitude for frequencies below 250-300 cycles. The con- 
clusion is that there is no real necessity for altering the character of 
the cut from constant velocity to constant amplitudes at this low 
frequency. If the "standard" cut is maintained at constant velocity 
amplitude for the entire spectrum the greatest danger of "over- 
cutting" would still occur in the neighborhood of 300 cycles, just as 
under the present "standard" conditions, but it would then become 
unnecessary to provide electrical equalization for the range below 
300 cycles, as is at present required with high-fidelity recording and 
reproducing equipment. 

A third conclusion and recommendation may be based upon a pos- 

Aug., 1938] 



sible modification of the ''standard" groove cross-sectional shape 
used in lateral recording. It seems almost certain that a lateral 
reproducer having the necessary vertical mobility assumed in the 
foregoing analysis can be designed to exert extremely light forces 
upon the groove wall. If this feature of the design can be carried far 
enough there is no reason why the needle tip radius may not be re- 
duced to less than 1 mil. If these conditions are satisfied there is 
then no necessity for (a) a total groove depth of 2.5 mils, or (b) such 
a large rounded bottom portion of the groove. For example, a sharp 
bottomed (or very slightly rounded) groove 2 mils wide should be 
adequate to provide tracking for a reproducer capable of operating 
satisfactorily with a stylus tip radius of 0.75 mil. If the desired 
maximum amplitude of groove modulation be retained at 2 mils, 
there would be a net saving of some 40 per cent of the available rec- 
ord surface, so that a groove pitch of 175 per inch could be used. 


Playing Time in Minutes 

Size and 
Speed of 

r = 2 Mils 
100 Grooves/ 

r = 0.75 Mil 
175 Grooves/ 

r = 2 Mils 
100 Grooves/ 

r = 0.75 Mil 
175 Grooves/ 

10-per cent distortion 

5-per cent distortion 

10" 78 rpm. 





12" 78 rpm. 





16" 78 rpm. 





12" 33 rpm. 





16" 33 rpm. 





Such groove spacing would allow as much as 30 minutes of recording 
on each side of a 16-inch, 33 rpm. transcription record, with no sacri- 
fice in the present available recorded levels, and with a material re- 
duction in total harmonic and cross-modulation distortion compared 
with present transcription records. For a 12-inch, 78-rpm. record 
suitable for home use a total of 11 minutes of recording would be 
available with a similar reduction in total distortion as compared 
with current practice. These reductions in harmonic distortion and 
the gain in length of playing time stem principally from the reduction 
in radius of the needle tip and the consequent desirability of reducing 
the width of the recorded groove at the record surface. Table I 
exhibits a comparison of the playing times available with a 10-per 
cent and a 5-per cent distortion limit, for lateral-cut records. 

180 J. A. PIERCE AND F. V. HUNT [j. s. M. P. E. 

The gain in playing time and usefulness of the convenient 12-inch, 
33-rpm. record is worthy of note, as is the fact that the lower the 
permissible distortion the greater is the advantage of the proposed 
narrow groove and small stylus tip. 

To achieve comparable reductions in distortion for the present type 
of standard, round-bottomed, lateral-cut groove, Mr. Olney has sug- 
gested to us the possibility of using a needle tip having either an 
elliptical cross-section presenting a small radius of curvature to the 
groove wall, or, alternatively, a needle tip section consisting of a flat 
circular disk perpendicular to the groove axis with the edges rounded 
to a small radius. 

Because this study has enabled us to predict the conditions neces- 
sary to its success, we wish to call attention here to the system of 
controlled volume expansion illustrated in Fig. 10. This method has 
been proposed before as a means of avoiding volume distortion, but 
it does not appear to have made its way into the art as yet. 

As the figure indicates, the only modification necessary in the 
recording technic is the introduction of a constant tone at a point 
in the system preceding the gain control which is used to compress 
the program material. This pilot tone must be of such a frequency 
that it is within the pass-band of the recorder and reproducer, but 
outside of the desired program band. In the diagram we suggest a 
12-kc. pilot tone, to be used with a 10-kc. program channel. No 
other change need be made in the recording technic. 

When such a record is reproduced with conventional equipment 
not responsive to the high-frequency pilot tone the performance is 
entirely normal and the user need not be aware that the record is in 
any way unusual. This seems to be an important feature since the 
pilot tone could be introduced in commercial records without impair- 
ing their value for use with existing phonographs. On the other hand, 
if the user wishes to take advantage of the enhanced volume range it 
is necessary only to employ a reproducer capable of responding to 
frequencies as high as that of the pilot tone, to segregate the pilot 
tone with a filter, rectify it, and apply it to the automatic volume 
control circuit of an amplifier similar to those ordinarily used in radio 
receivers. This automatic volume control operates to maintain a 
constant level of the pilot tone at the amplifier output. Since this 
condition is that which obtained during recording, the original volume 
range will have been restored. That this is possible may be made 
clearer by consideration of the fact that we now have two independent 

Aug., 1938] 



recorded and reproduced channels, operating in synchronism. By 
proper use of these two channels we are able to add their volume 
ranges while listening to the program material carried by one of them. 
The ka-kr chart of Fig. 4 indicates that the high-frequency pilot 
tone will be subject to considerable distortion (and cross-modulation 
with the program material) unless it is recorded at a level substanti- 
ally less than that of the program. In spite of this restriction the 
effective signal-to-noise ratio for the pilot channel may be as high as 
for the program channel if the control-tone is separated out with a 
filter whose pass-band is no wider than necessary to guard against 



to AU 












FIG. 10. Diagram illustrating system for controlled 
volume expansion, capable of restoring full dynamic 
range of original program material. 

variations in turntable speed, and if the time-constant of the auto- 
matic volume control circuit is large enough to smooth out the irregu- 
larities of surface noise. 

In brief, such a system of controlled volume expansion can fur- 
nish an accurate complement to the compression necessary in record- 
ing, and provide for the re-creation of the desired program in its full 
dynamic range. At the same time, it should be emphasized that such 
records would remain as satisfactory as any of those in common use 
when reproducing facilities for expansion are not available. 

As an alternative method of utilizing a second recorded channel, 
it may be pointed out that if it is undesirable to re-create the full 
dynamic range of the original material the control channel may be 
used to provide volume inflection while the program is recorded well 

182 J. A. PIERCE AND F. V. HUNT [j. s. M. P. E. 

above noise level at all times. While such records could be used only 
with reproducing equipment designed especially for them, they would 
provide phonographic reproductions entirely free from the audible 
effects of surface noise. 

In conclusion it may be said that a principal result of this study 
has been the recognition and analysis of a large latent advantage, 
with regard to distortion, inherent in the lateral type of groove modu- 
lation. While not all these indicated gains are realized by the pres- 
ent conventional lateral-cut technic, we hope that new reproducer 
designs and a study of these geometrical relations will furnish some 
guidance for significant improvements in the fidelity and usefulness of 
disk records. 


1 OLNEY, B.: Electronics (Nov., 1937), p. 19. 

2 DiToRO, M. J.: "Distortion in the Reproduction of Hill-and-Dale Record- 
ings," /. Soc. Mot. Pict. Eng., XXIX (Nov., 1937), No. 5, p. 493. 

3 CHAFFBE, E. L.: Rev. Sci. Instr., 7 (1936), p. 384. 

4 SIVIAN, DUNN, AND WHITE: /. Acoust. Soc. Amer., 2 (1931), p. 330. 
FLETCHER, H.: Bell Syst. Tech. J., 3 (1931), p. 349; Rev. Mod. Phys., 3 

(1931), p. 258; J. Acoust. Soc. Amer., 3 (1931), Supp., p. 1. 

5 HUNT, F. V., AND PIERCE, J. A: Electronics, 11 (1938), p. 9. 


MR. MACNAIR: The kind of distortion on hill-and-dale records that was 
analyzed in the paper was discussed qualitatively at the Fall, 1931, Meeting of 
the Society (/. Soc. Mot. Pic. Eng., Feb., 1932, p. 143). A quantitative analysis 
of it appeared last year, and again we have a beautiful analysis of the subject 
presented to us this morning. 

In Fig. 1 the lower curve is a sine wave, showing the shape of the bottom of a 
groove cut in a hill-and-dale record. When a stylus of finite radius traces the sine 
curve, there appears in the electrical output of the reproducer a signal correspond- 
ing to the upper curve having the characteristics that were mentioned by Mr. 
Pierce, namely, broad on the top and sharp at the bottom. It is therefore not 
a sine wave, and contains certain distortion products that were not in the original 
cut record. 

There are several possible ways to correct for this kind of distortion. One is 
simply to dubb with the circuits poled properly. If one records the signal picked 
up from the reproducer, this upper shaped wave is recorded in the wax. But in 
doing this the circuit should be properly poled so as to cut the signal in the wax 
as illustrated by turning Fig. 1 upside down. If the last record is now traced with 
a stylus of the same size, the signal reproduced will be the original sine wave. 

What has been done, then, is, when playing the record, to get from the re- 
producer a signal that is, so far as this kind of distortion is concerned, exactly the 
sine wave with which you started, a true picture of the originally recorded signal. 


There are other possible ways to take care of this distortion, but the way de- 
scribed, namely, a dubbing process with the circuits properly poled, is the easiest 
to present here. Whether the distortions are of an objectionable magnitude de- 
pends, as the author pointed out, upon the recording, the level, and other con- 
ditions of the process, and also upon the purposes for which the recorded material 
is to be used. This method of greatly reducing this form of distortion has been 
available for some years. 

MR. PIERCE: In order properly to reverse the poid this way it is, of course, 
necessary to have a transmission band that will pass all the harmonics generated 
in the original poid. In the extremely high-frequency cases, 5000-10,000 cycles, 
it may well require fourth and fifth harmonics in order to do this, which calls for 
a recording technic of rather remarkable excellence to do it properly. 

A rather worse objection is that cross-modulation products, sum and difference 
tones (particularly difference tones), appear in the output through this phenome- 
non. They are rather difficult to analyze, but may be taken as more or less of the 
order of magnitude of the harmonic distortion. However, it is impossible to re- 
produce these cross-modulation products accurately the second time by this dub- 
bing procedure, which is very unfortunate because they are the worst offenders so 
far as hearing is concerned. Ten to 15 per cent of pure harmonic content is toler- 
able, but when signals having those energies appear at random frequencies not 
associated with the material being reproduced, the effect upon the ear is a familiar 
burring, an unpleasant form of distortion that is heard when a commercial record 
is played through a 10,000-cycle channel, a way it is not originally intended to be 

MR. COOK: Have you investigated the magnitude of the distortion which 
might result from a lack of needle tangency to the record groove? 

MR. PIERCE: Not very much, except to investigate it experimentally. We 
found it was not a very serious subject on play-back, but did make quite a bit of 
difference in recording. Mr. Olney has made a rather good analysis of the subject, 
published, I think, in Electronics last year, which indicates that with reasonable 
precaution it can be kept down so well as to be practically out of the picture. 

MR. COOK: I assume you refer to the use of an offset pick-up head placed at 
an angle to the tone-arm. It is interesting to note that both these expedients 
were employed by the Brunswick, Balke, Collender Co. who, it is believed, first 
proposed and used them in their first commercial electrical phonographs. 

MR. PIERCE: That form of correction is entirely applicable. I might point 
out one other thing that Mr. Olney has suggested, which is the use of stylus tips of 
non-spherical shape, so that they present to the edge of the groove a smaller 
radius than they have in other dimensions. 

MR. COOK: I was interested in your recommendation for the use of a control 
tone. My first acquaintance with it was while with the RCA. The results they 
obtained were impressive and, as Mr. Pierce has reported, it represents a desir- 
able improvement. Their work with it was mentioned at the 1935 Spring Con- 
vention in Hollywood in a paper entitled "A Consideration of Some Special 
Methods for Re-Recording," J. Soc. Mot. Pict. Eng., XXV (Dec., 1935), No. 6, 
p. 523. 

MR. PIERCE: It can be added to present technics so simply that it is worth 
thinking about. 

184 J. A. PIERCE AND F. V. HUNT [j. s. M. P. E. 

MR. DAVEE: For the past two and one-half years or so I have been connected 
with the World Broadcasting Company. You probably have heard their tran- 
scribed records over the radio, probably the program of Chevrolet with Graham 
MacNamee. I did not appreciate that this burring sound you are discussing 
was there. In all program work of that kind a certain amount of re-recording and 
dubbing has to be done, as in motion picture work, and as a result we have been 
using this poled dubbing scheme regularly. 

MR. KELLOGG: The correction obtainable by correctly poled dubbing, or by 
any method that attempts to precompensate and give back the desired wave, 
involves some extreme difficulties, and while I would not for a moment deny that 
with reasonably good channels it would always be helpful, I had not, until this 
morning, realized that it has ever been practically applied, unless the dubbing 
were necessary for other purposes. It involves, for example, such difficulties as 
providing (when you reach the limiting curvature) infinite acceleration of the 
cutting stylus. 

In lateral recording it appears that an analysis based upon purely geometrical 
relations leaves out so many important factors that its predictions can not be veri- 
fied by tests. 

MR. HASBROUCK: In Fig. 2 I noticed that the stylus was shown as not reaching 
the bottom of the groove. The groove that we use, and which is generally used 
for transcription work, has a radius at the bottom. The straight sides are rather 
short compared with the radius, and we attempt to contact the spherical portion 
of the stylus completely on the bottom. In that way we distribute the weight 
most uniformly and reduce wear and so forth. 

I wonder whether any improvement is found in riding the straight sides of the 
groove, and whether it would not increase the wear on the record as well as dis- 
tortion. The question of cold flow of the record material was not mentioned. 
It is quite pronounced; so much so, in fact, that a pick-up that has one frequency 
characteristic on one record material will have another frequency characteristic 
on another record material, depending upon the hardness. On these new in- 
stantaneous records, with fairly soft material, we have found it very annoying. 

Also, as regards the high-frequency losses, a small playing diameter increases 
them very greatly, particularly with soft record material. That would seem to 
interfere with the control tone idea to some extent. We have measured losses at 
10,000 cycles on nitrate lacquer amounting to some 28 db., playing from an 
8-inch diameter to a 16-inch diameter. While that could be compensated for to 
some extent in recording, I wonder whether it would not make the control tone 
idea more complicated. 

MR. MACNAIR: This discussion may have given the impression that correcting 
distortion of this type is very complicated. Many of you do something similar 
in the motion picture business every day. If the harmonic content of a variable- 
density negative is analyzed, harmonics and cross-modulation products will be 
found in abundance. These are eliminated by the simple process of printing, 
and certainly we do not claim to print 40,000 cycles very well. There are two ways 
of looking at these problems. The analysis into harmonic components is the more 
appropriate one for some problems, and the simple consideration of returning the 
wave shape to its original is another way of looking at it. 

The micromatics of harmonic analysis for this problem leads to great complica- 


tion, and it happens that the other way of looking at it is the simple way. 

MR. PIERCE: Mr. Davee's remarks point out admirably the fact that our 
established amplitudes of cut, frequency response, record speed, stylus tip radius, 
and so on, are all so interrelated as to give a pleasing result. The types of distor- 
tion with which we are particularly concerned here are most readily observable 
when standard commercial records are played through a really high-fidelity 
system. In case Mr. Davee is really anxious to observe the distortions, we sug- 
gest that he try listening only to the frequency band between 5000 and 10,000 or 
12,000 cycles. 

I think that Mr. Kellogg has answered Mr. MacNair more aptly than I was 
able to do. The effect of compensating by properly poled dubbing seems to put 
the system in push-pull with the pull appearing as a separate episode from the 
push. It is obvious that this is a difficult technic to handle and it is hard to see 
how the final result can be better than it is in the case where we have a truly push- 
pull system. We are under the impression that this poled dubbing technic is not 
used as standard practice, so that many vertical-cut records are released without 
its advantages. Mr. Kellogg's concluding remarks about the inadequacy of 
geometrical analysis seems to be effectively answered by the data exhibited in 
our Fig. 9. It is true that other factors may become important unless the re- 
producer meets the requirements we have discussed in the paper. 

The condition that troubles Mr. Hasbrouck has been chosen deliberately, and 
the illustration to which he refers is a fairly accurate representation of the geomet- 
rical conditions obtaining in our equipment. As we have explained, this is done to 
prevent distortion due to "rattling" of the stylus; in other words, to provide posi- 
tive drive for the stylus which is following a laterally modulated groove. It is 
true that the pressures at the points of contact are greater than they would be if 
the stylus rested in the bottom of the groove, but it is possible to build a reproducer 
that will not deform the record material even when such a condition exists. As 
we have pointed out, this is necessary in order to permit us to calculate distor- 
tion. We believe that the distortion so calculated will be at least no greater than 
that caused by allowing the needle tip to trace a random course that we can not 
examine analytically. The necessary requirement in this case is that the stylus 
must execute a vertical motion without generating a corresponding electrical 

We have been able to show experimentally that instantaneous cold flow of the 
record material is not an important factor when a sufficiently light reproducer is 
used. A simple and adequate way of checking this fact is by making a frequency- 
response record and playing it at more than one speed, such at an 33 Vs and 78 
rpm. When the record speed is varied in this way the output at all corresponding 
frequencies should change by a constant factor. When this is the case it indicates 
that the reproducer stylus is not deforming the record material either temporarily 
or permanently. 

Variations in hardness of the record material can affect the frequency character- 
istic only because many cutting heads depend upon the record material for at 
least part of their damping. Thus the amplitude of the cut is a function of fre- 
quency, record hardness, and linear groove speed, instead of frequency alone. In 
the best cutting heads, this effect is practically negligible. As we have shown in 
the paper, any variation in frequency response over the record surface is an indica- 


tion either of a poor cutting head or of too great cutting levels. Variations in 
amplitude upon playback, of 28 db., corresponding to only a 2:1 variation in 
linear groove speed seem startling to us and are a strong indication of some serious 
condition that should be corrected. 

Mr. MacNair's final argument is beautifully expressed and seems plausible 
but will not bear close inspection. Regardless of the argument used, it is im- 
possible to change the physical fact that transmission of the complete band cor- 
responding to the original poids, that is, all high harmonics and cross-modulation 
products, is so difficult as to be practically impossible. Mr. MacNair will agree, 
I am sure, that, if we can reproduce only a difference tone because the sum of two 
high frequencies lies outside the transmission band, it is impossible to restore the 
original two tones by his poled dubbing technic without leaving distortion in the 
final product. We realize that correction of this sort for vertically cut records is 
decidedly beneficial and may even, if properly executed, produce a final result 
comparable to that which is easily obtained with lateral groove modulation. Al- 
though the technic has certain apparent disadvantages, we regret that it is not 
used more consistently in commercial practice. 



Summary. In motion picture projection optical systems for tungsten-filament 
sources, the condenser design is such that the source is imaged well ahead of the picture 
aperture. This position is dictated by considerations of uniformity of screen bright- 
ness. It is not the optimal position from the standpoint of utilization of light, for it 
entails losses at the aperture. At the best position for efficiency, the degree of brightness 
uniformity is inacceptable because of the non-uniform brightness of the source. The 
paper describes a method for reducing such losses without sacrificing picture quality. 

The design requirements of optical systems for picture projection 
have been well defined in technical papers presented before the 
Society over the years. It is well known, for example, that to achieve 
uniformity of lighting of the screen the condenser diameter and con- 
denser-aperture spacing must be such that upon looking backward 
through the projection system from all points on the screen one will 
see equal ares of uniform brightness. In practice that is not com- 
pletely realized at the margins because of vignetting by the projection 
lens tube. 

Given a source of uniform brightness, uniform illumination of the 
screen is achieved with greatest efficiency in light utilization if the 
image of the source formed by the condensing lens lies slightly ahead 
of the aperture. When, as in Fig. I (A), the image is formed at the 
aperture, the light lost at this gate is at a minimum. However, the 
divergence of the beam is then so great that much of the light is not 
intercepted and transmitted by the projection lens. As the source 
image is moved farther ahead, Fig. 1 (J5), aperture losses increase but 
a greater proportion of the remaining light is transmitted by the 
projection lens. It is apparent that for any given combination of 
condenser-aperture spacing, aperture size, and projection lens, there 
is an optimal position where the sum of the two losses is at a minimum. 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 15, 1938. 

** General Electric Co., Cleveland, Ohio. 




[J. S. M. P. E. 

If the source be non-uniform in brightness, the image formed by the 
condensing lens will also be non-uniform. It is the degree of uniformity 
across the beam at the picture aperture that determines whether the 
screen is acceptably illuminated; and this uniformity increases as 
the position of the image is moved forward from the aperture. In 
practice the image has, accordingly, been placed a considerable dis- 
tance from the point of optimal utilization of light. This paper deals 
with means for minimizing the losses that have heretofore been thus 

In order to determine the effect of image position upon net output 
of projectors, tests were made with five typical optical systems of 



FIG. 1. Effect of position of source image upon light losses at pic- 
ture aperture and at projection lens. 

the 16-mm. size. The condensers employed included the usual spheric 
types as well as aspheric combinations. The light-source was an 
incandescent filament lamp of the conventional biplane construction, 
and of such size as to insure that the system was always completely 

Various image positions along the optical axis were attained by 
changing the focal length of the condensers. In the case of the spheric 
combinations, and in the aspheric systems combining all corrections 
in one lens, this was accomplished simply by substitution in the 
element nearest the aperture. In one system, in which both elements 
are aspheric, the focal length of the combination was changed by 
introducing a third element of appropriate focal length mounted 
close to the lens nearest the aperture. 















5 S 2 S 









" - 






10 O 10 20 30 40 50 60 70 00 90 101 


FIG. 2. Relation of position of source image to screen 
illumination for 16-mm. projection systems with aspheric 

60 00 

FIG. 3. Relation of position of source image to level 
of screen illumination for 16-mm. projection systems with 
spheric condensers. 

190 F. E. CARLSON [j. s. M. P. E. 

The results of these tests are shown graphically in Figs. 2 and 3. 
While the data apply only to the five optical systems tested, they 
indicate the order of the penalty imposed by non-uniformity of source 
in projectors generally, whether of the 8-mm., 16-mm., or 35-mm. 
size. The standard position of the source image for each of the equip- 
ments tested is noted on the curves. It will be observed that in the 
aspheric systems the net output actually utilized is 16 to 25 per cent 
below the maximum possible, and that for spheric condensers it runs 
to nearly 40 per cent below. 

Fig. 4 shows, in A and B, respectively, the approximate appearance 
of the screen when the image is focused at the point of maximum 

FIG. 4. Appearance of screen when source is imaged (.4) at point of maxi- 
mum light output, and (B) at standard positions indicated in Figs. 2 and 3. 

light output and at the positions actually used in practice. It will be 
seen that the lack of uniformity is evidenced crosswise of the screen, 
not vertically. In other words, so far as uniformity of brightness 
from top to bottom of screen is concerned, the source could be imaged 
close to the position of maximum output. 

It has been standard practice to focus both dimensions of the source 
in the same plane. It is not necessary that that be done. A more 
rational procedure would be to incorporate a cylindrical or toric 
surface in the condensing system to provide a differential in the dis- 
tance at which the vertical and horizontal dimensions of the source 
are focused. Such structures are commercially feasible. Cylindrical 
surfaces have, for example, been used to give the beam from a cir- 
cular source an approximately elliptical cross-section in order to fit 
it more nearly to the dimensions of a particular aperture. If, now, 






FIG. 5. A few of the methods available for incorporating cylindrical or 
toric surfaces in typical condensing systems for differential focusing of width 
and height of source. 

192 F. E. CARLSON fj. s. M. P. E. 

the structure is instead adapted to focus one dimension of a rec- 
tangular source in the plane of maximum output and the other di- 
mension in the nearest plane for which uniform illumination results 
at the aperture, considerable gain in output can be achieved at the 
same time that uniformity of screen brightness is preserved. 

Fig. 5 illustrates three of a number of possible modifications of 
representative types of condensing systems to accomplish the differ- 



FIG. 6. Increase in light output obtained by incor- 
porating cylindrical or toric surface in condenser. 

The height of the column represents, for each of three 
equipments, the net light output with source imaged at 
position for maximum light utilization, disregarding 
uniformity of screen. The black portion represents the 
part of the possible output realized in equipment as now 
made. The shaded blocks show the gain when con- 
densers are modified as described. 

The three columns are not to the same scale and 
therefore are not to be compared with each other as to 
absolute values. 

ential focusing. A shows the simple case of substituting a cylindrical 
for a plane surface of a combination, thus producing a lens of shorter 
focal length in the meridian corresponding to the length of the coils 
of the lamp. In B the cylinder is concave instead of convex in order 
to increase the focal length of the meridian corresponding to the 
position at right angles to the coils of the lamp. If all the surfaces 
of the combination were spheric or aspheric one would provide, in 
place of the cylindrical surfaces illustrated, corresponding convex 
and concave toric surfaces. In C, two cylindrical (or toric) surfaces 


with their axes 90 degrees to each other are u c 1 produce a differ- 
ential in strength or focal length in these two meridians. 

Lenses were made incorporating these p .pies, but otherwise 
identical with those employed in the above tests of conventional 
systems. They were tested in three of the equipments, all representa- 
tive of the high-quality group of 16-mm. projectors, with results as 
charted in Fig. 6. The increase in net output of the projectors varied 
from a minimum of 12 per cent for an aspheric, to 25 per cent for a 
spheric system. Factors affecting the realizable gain in efficiency 
include the angle of acceptance and the relative aperture and focal 
length of the projection lens, as well as the condenser-aperture spacing. 


MR. KELLOGG: Your analysis and estimate of gain are based upon the sup- 
position that you have a large enough projection lens to collect all the light that 
gets through the aperture; in other words, that you fill the lens with the filament 
image at all times? 

MR. CARLSON: The gains shown are measurements and not e,< ^d values, 

and there has been no change in any of the optical systems other an in the focal 
length of the condensing lens. That is, the projection lens was r t changed nor 
was its position changed. 

I doubt that projection lenses, even when used with conde iv^ng systems de- 
signed in accordance with present practice, collect and redirect to the screen all 
the light that gets through the aperture. Ignoring surface losses, there is usually 
some obstruction to marginal rays, varying in amount with the angle these rays 
bear to the optical axis. The reason we obtain a gain in screen illumination is 
that we are working at the point where the sum of the losses at the projection 
lens and at the aperture is reduced. 

MR. KELLOGG: Would not your story be changed if you assumed a smaller 
projection lens? You are assuming, are you not, about as fast a projection lens 
as is practically available? 

MR. CARLSON: Not necessarily. The data for each optical system tested 
were not included in the charts shown, but there were also tested in the course 
of the earlier experiments optical systems incorporating f/2 projection lenses in- 
stead of //1. 65, and the same relative gains seem to apply. 


R. M. EVANS** 

Summary. In subtractive color processes it is desirable to have some type of sensi- 
tometry to tell how the process departs from correct rendering of neutral gray scales. 
Reading the density of a color deposit through an arbitrary filter does not give rise to 
a useful value in terms of the final color process. For practical use the "effective den- 
sity'' of a color is defined as the visual density produced by adding sufficient of the 
other colors of the process to produce gray. An instrument is described that reads 
such values directly. This instrument is capable also of analyzing the amounts of 
each of two or more colors when present simultaneously and permits the analysis of a 
sensitometric exposure into the corresponding deposits of each color. Complete 
sensitometric curves may be drawn for all the records from the readings of a single 

In all processes of subtractive color photography, the problem of 
so "balancing" the individual color records that the requirements of 
best tone reproduction are realized is rather difficult. A large part 
of the difficulty arises from the lack of suitable means for measuring 
and specifying the actual amounts of image-forming material in each 
record individually. Once these amounts are measured, however, 
there still remains the problem of determining the relationships be- 
tween them that will produce the required results. 

The conventional methods of colorimetry may always be applied 
to any color process, either for each layer or for the process as a whole. 
Such methods, however, are concerned primarily with the later stages 
in which the final colors may be compared to the original subject. 
For this purpose, no substitute is known or needed and the subject 
need not here be discussed further. 

In the earlier stages when any color process is being worked out or 
being brought under control, there usually exists a need for the 
equivalent in colors of black-and-white sensitometry. It is a usually 
accepted axiom of color photography that the colors used and the 

*Received June 6, 1938. Communication No. 676 from the Kodak Research 

** Eastman Kodak Co., Rochester, N. Y. 



mode of operation of any process must make it possible to reproduce 
a scale of neutral grays as such, unless a fourth record in gray is to 
be added to the image. Even in this case a close approximation to 
this condition is necessary. 

The methods of sensitometry apply directly to such a gray scale 
and the reproduction of such a scale is usually considered to define 
the tone or brightness reproduction possibilities of the process. In 
other words, the brightness reproduction scale of the process is as- 
sumed to be denned by the brightness reproduction of a scale of 
neutral grays. In reality, such an assumption is not justified for any 
part of the reproduction except that of gray scales, and it obviously 
has nothing to say about the reproduction of hue or saturation of 
colors. That that is true is obvious from the fact that three colors 
that are each very similar to gray might be used and the reproduction 
of a scale of grays made practically perfect without aiming at a color 
process worthy of the name. 

The present paper is concerned with subtractive color processes in 
which the individual colors used for the part images are considered 
satisfactory in themselves. Consideration will be given only to the 
measurement of each color record in such a way that it is directly 
apparent how much of each is necessary to form a gray of the re- 
quired density. 

The statement is found frequently in the literature of color photog- 
raphy that one of the important requirements of a subtractive color 
process is that the contrast or "gamma" of all the color records 
shall be the same. In general principle, this requirement is obvious 
enough, but further consideration shows that it is a rather vague con- 
cept unless new definitions are made for density and gamma. 

In the sensitometry of ordinary silver processes in which the images 
are essentially gray, the term "density" is defined as the logarithm 
of the reciprocal of the transmissions of the deposit. It is usually 
assumed that the transmission is measured visually, but that is not 
entirely necessary since the deposit is usually so uniform in its trans- 
mission of light of all colors that the sensitivity of the eye to color 
does not come into the problem as a large variable. "Gamma" is 
then defined as the slope of the line in a plot of density against the 
logarithm of the exposure that caused it. In other words, it is the 
ratio of cause to effect, and as such is an extremely useful concept. 
The requirement stated above for color processes, then, is that 
the ratio of cause to effect shall be the same for each color record. 



[J. S. M. P. E. 

The three colors are assumed, whether correctly or not, to give gray 
when present in equal amounts. This latter assumption is not true 
in the case of most practical processes. What is wanted, then, is a 
method of measuring the color deposits constituting each color record, 
in such a way that the quantity of each color appears equal when the 
colors superimposed give a visual gray. If each record could be read 
in terms of "density," then, when the density of each of the color 
records was the same, the result of superimposing the colors would 
be gray. The "gamma" of each record, defined in terms of these 
densities, would then each be the same when the process was repro- 
ducing a gray scale. This result may be accomplished by defining a 
new kind of density which might be called the "equivalent density" 

500 600 


FIG. 1. Effect of impurities upon combined 

of a color. We may define this as follows: The "equivalent density" 
of a color in any subtractive color process is the visual density it would 
have if it were converted to a neutral gray by superimposing the just- 
required amounts of the fundamental colors of the process. The defini- 
tion appears as if it might be extended to any color independent of 
a color process and defined as the density that a color would have if 
it were subtractively combined with its exact physical complementary. 
Such an extension of the definition, however, does not lead to the 
same result. This may be demonstrated by an example. 

If three practical dyes are chosen which in a certain ratio give 
neutral gray, the visual density of this gray is greater than the maxi- 
mum absorption density of any one of the dyes at any wavelength. 
This is due to the so-called "impurity" of the colors, and is illustrated 
by the arbitrarily drawn curves of Fig 1. In this figure the density 
of each dye at each wavelength of light in the spectrum is plotted 


separately, the density at each wavelength being defined as in the 
case of silver images. (This is possible because the relative sensitivity 
of the eye to different wavelengths does not enter.) The density at 
each wavelength for the three dyes combined may then be obtained 
by adding the three curves at each wavelength, just as neutral densi- 
ties may be added. Since the three dyes have been chosen to give 
a neutral gray when mixed, the point-by-point addition of the curves 
gives rise to a fourth curve which is at essentially the same density 
at all wavelengths. Being the same at all wavelengths, this density 
is the value that would be read by white light on a densitometer. 
Note, however, that since each of the dyes had a definite density at 
every wavelength, the final neutral density is higher than any point 
in any of the curves. If the exact physical complementary for any of 
the dyes were added to that dye, nothing would have been added to 
its maximum density and the final neutral density would have been 
less in such a case than in the case of the three actual dyes. 

Furthermore, the term "complementary" color as used here could 
apply only to a given dye at a given concentration, and would require 
to be changed if the concentration of the dye in question were changed. 
It is for these reasons that the density of a dye deposit as determined 
by reading it through an arbitrary filter on a visual densitometer 
does not lead to density readings that are directly significant for a 
process in which the dye is used. 

It is apparent from what has been said above that the density 
curve for any individual color record in a subtractive process may be 
obtained readily by determining the densities formed when sufficient 
amounts of the other two colors are superimposed on each step to 
form a neutral gray. The densities so determined have the property 
that when equal densities of all the colors are superimposed the result 
is a neutral gray whose density is equal to that of each record. In 
other words, if the densities are so determined, the sensitometric 
curves for each record must have the same slope or gamma and must 
lie in the same position with respect to the exposure axis in order 
that the process shall reproduce a scale of neutrals as a scale of 

A simple instrument has been devised for the purpose of measuring 
densities according to the above definition. In principle it is similar 
to that of the Capstaff-Purdy densitometer 1 now widely used in the 
motion picture industry. In this well known instrument the image 
whose density it is desired to determine is placed in a beam of light 



[J. S. M. P. E. 

in series with a circular neutral gray wedge whose densities are 
known at every point. By another path, light from the same source 
is brought around the wedge and both beams of light enter an eyepiece 
in such a way that comparison of the brightnesses of the two may be 
made to high precision. The brightness of the unimpeded beam, due 
to the length of its path, is made less than that of the wedge beam in 

FIG. 2. Schematic arrangement of color densitometer. 

a known ratio. In other words, it requires a definite density of, say, 
3.4 in the path of the light through the wedge to make it equal to 
brightness of the comparison beam. The density of the unknown 
sample may be determined by moving the wedge until the two beams 
match. At this point it is known that the sum of the density of the 
wedge and the unknown equals 3.4, and the instrument may be cali- 
brated to read the difference between this and the actual wedge den- 
sity, or the density of the unknown. The great advantage of this 


type of instrument, aside from its simplicity, lies in the fact that the 
actual brightness of the field when the two beams are matched is 
always the same. 

The present instrument retains this feature and has, as well, the 
important feature for visual color work that both fields are neutral 
at the balance point. 

The design of the instrument is as follows : In a densitometer with 
an optical system similar to that of the Capstaff-Purdy instrument 
there is placed in the beam of light passing through the wedge a color 
wedge for each color of the process formed by the color process for which 
the instrument is to be used. If it is a three-color process there will 
be three color wedges in addition to the gray wedge of the usual in- 
strument. Fig. 2 shows the instrument diagrammatically. 

To measure the density of a color deposit the film carrying the color 
is placed in the beam C with all wedges set at maximum transmission. 
The brightnesses of the two halves of the field are then roughly 
matched by rotating the neutral wedge. Considering for the moment 
that the color being measured is that of one of the color records only, 
each of the other two wedges is rotated until the transmitted light is 
gray. The brightnesses of the two halves of the field are then matched 
and the exact density is then read from the scale of the neutral wedge. 
In actual practice the balancing operation is only slightly more 
difficult than in the case of the single- wedge instruments. 

If the color is not a deposit of one color record alone but is a mix- 
ture of two or of all the records, the density may still be determined 
and is of equal validity to that read from a deposit of a single color 
if care is taken to add in only those colors in which the original is 
deficient. Where the density corresponding to one color record is all 
that is desired there is no need for calibration of any of the color 
wedges. It is within the capacities of the instrument, however, to 
calibrate itself, and when this is done it becomes possible to de- 
termine the equivalent density of each of the colors in any mixture. 
This makes it possible to determine the curves for each color record 
from a single photograph of a neutral scale or, more conveniently, 
from a single exposure to white light in a sensitometer of the con- 
ventional type. 

The calibration and application of the instrument for this purpose 
are carried out as follows : Arbitrary scales are attached to each of 
the color wedges. If wedge C is to be calibrated, it is set at the first 
division of its arbitrary scale, say, ten degrees from the point at which 



[J. S. M. P. E. 

the wedge has no color. The other two wedges are then rotated until 
the light passing through is gray, the brightness of the beam is 
matched to that of the comparison beam, and the "equivalent 
density" read from the neutral wedge is applied to the wedge being 
measured. In other words, each wedge at successive points is con- 
sidered as a sample to be measured, and in this way each is calibrated. 
Any color may now be specified in terms of the equivalent densities 
of each of its components. To do this the sample is placed in the 
beam as usual ; the wedge corresponding in color to the predominant 
color of the sample is left at zero, and sufficient of each of the other 

FIG. 3. Color density curves of a sensitometric strip. 

colors is added by means of the wedges to give a neutral which is then 
balanced with the neutral wedge. The neutral wedge now reads the 
equivalent density of the color present in the greatest amount, and 
the densities on the other two wedges, subtracted from this value, 
give the equivalent density of each of the other colors present in the 

If a sensitometer strip is exposed by white light and the resulting 
steps are read on the instrument, the curves of each color may be 
plotted independently. Such curves, read on an instrument built 
according to the above scheme are shown in Fig. 3. They are chosen 
deliberately to show a color process not balanced for reproduction in 
gray of a neutral scale. The strip appeared neutral on step A , red 
at step B, and green at step C. 


A slight modification of the instrument may be necessary in the 
case of some processes, particularly if the deposits for each color are 
highly diffusing. In this case the addition of spherical lenses between 
the color wedges as shown in Fig. 2 may be necessary. In any case 
the addition of such lenses will increase the light transmission of the 
instrument. The instrument depends for its successful operation, 
particularly if the color wedges are to be calibrated, upon the inter- 
changeability of any color at the wedge and at the position of the 
sample. This is readily tested by reading a series of color deposits 
separately and then superimposed. An actual instrument built in 
the Kodak Research Laboratories for a process employing dye 
images has been highly successful and meets the requirement of 
additivity well within the required precision. Finally, it must be 
emphasized that such an instrument must be fitted to each particular 
process, the wedges being made by the process, and the interchange- 
ability of colors at the wedge and sample positions must be checked 
over a sufficient range before the results can be expected to yield 
useful information in the control and adjustment of the process. 

The author acknowledges his thanks to his colleagues, Mr. George 
Silberstein and Dr. W. T. Hanson, Jr., the former for his painstaking 
construction of the first instrument and the latter for the additivity 
test necessary to determine the reliability of the instrument. 


1 CAPSTAFF, J. G., AND PURDY, R. A.: "A Compact Motion Picture Densitom- 
eter," Trans. Soc. Mot. Pict. Eng., XI (1927), No. 31, p. 607. 


Summary. The plan of work followed by the Papers Committee during the past 
couple of years is discussed, together with the results achieved by following the plan. 
The Report concludes with regulations of the Society with regard to the preparation of 
papers for presentation and publication, and detailed instructions concerning edi- 
torial style and typographical arrangement. 

The functions of the Papers Committee are two-fold: (1) to ar- 
range and supervise an appropriate program of papers for our semi- 
annual meetings ; (2) to secure an adequate number of papers to fill 
twelve issues of our JOURNAL during each year. Nearly 1400 mem- 
bers depend upon the Committee for the latter function; about 250 
for the former. 

There were 96 papers and 13 reports published in the JOURNAL 
during 1937. Out of this total of 109, only 8 were submitted di- 
rectly to the Editorial Board for publication ; 5 were reprinted from 
other publications, and 1 was read before a Local Section meeting. 
These 14 papers represent less than 13 per cent of the total, and 
should impress upon us the importance of having an adequate num- 
ber of papers at each semi-annual meeting to provide material for six 
issues of the JOURNAL. It indicates also that the majority of our 
membership are stimulated primarily to write papers when they plan 
to attend Conventions and not at other times. 

Two years ago, a plan was suggested by this Committee for the 
organization of its work. It consisted of the following steps: (1) 
publication of a request for papers in each issue of the JOURNAL for 
four months before the meeting, offering preferred positions on the 
program, with ample time for presentation and discussion, to those 
who turn in their manuscripts six weeks before the meeting; (2) 
personal solicitation of papers by members of the Committee; (3) 
publication of abstracts in the issue of the JOURNAL appearing im- 
mediately before the meeting; (4) request for manuscript copies 10 
days before the meeting. It has, in addition, been customary to cir- 
culate a Tentative Program about 3 weeks before the meeting as well 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
May 25, 1938. 



as to publish this Program in the number of the JOURNAL immedi- 
ately preceding the meeting. 

This plan has proved quite effective, as shown by the quality and 
number of papers presented at the last four meetings. Much 
work is necessary, however, to secure abstracts and manuscripts 
on time, but authors appear to have become more appreciative of the 
requirements and are making greater efforts to comply with the regu- 
lations. Some lack of understanding of the meaning of the term 
abstract has been found among a few authors ; others have said that it 
was unfair to request manuscript delivery before the meeting. 

An "abstract" may be defined as a digest of a paper, which states in 
clear, concise sentences the significant material discussed in the paper. 
Examples of good abstracts are included in the Special Bulletin of this 
Committee, supplementing this report. This Bulletin was drawn 
up two years ago and has been revised from time to time. It contains 
a summary of the administrative practices of the Society regarding ac- 
ceptance and preparation and oral delivery of manuscripts. It has 
been distributed to the majority of authors during the past two years 
and has proved of service to the authors as well as the editorial office. 
Several papers are received for each meeting, however, that do not 
comply with our regulations, and it is evident that the authors have 
not read or, perhaps, have not been aware, of the regulations, espe- 
cially those related to bibliography and footnote style, illustrations, 
and drawings. It is suggested, therefore, that wider distribution 
should be made of this Bulletin by publishing it in the JOURNAL as a 
supplement to this report. Reprints could then be obtained for cir- 
culation to authors who are not members of the Society. 

It has been customary to print the Preliminary Program both in the 
JOURNAL issued before the meeting and in leaflet form for distribution 
to all members and authors. A final, corrected program is also 
printed in the JOURNAL a month after the meeting. It seemed an 
unnecessary duplication to distribute the Preliminary Program twice, 
and with the approval of the Board of Governors, the Preliminary 
Program was omitted from the April, 1938, issue of the JOURNAL. 
Abstracts have been published, however, to facilitate discussion at 
the meeting and to provide a source of reference until the paper has 
been published. 

It is important that the Papers Committee should cooperate closely 
with the Publicity Committee, especially during the period just prior 
to and during the semi-annual meetings. Copies of all abstracts of 


papers are turned over to the Publicity Committee several weeks 
before the meeting, as well as details concerning special demonstra- 
tions or prominent speakers on our programs. 

Two years ago we began the practice of supplying the Chairman of 
the Publicity Committee with a copy of all available manuscripts for 
his use during the period of the Convention. This plan proved 
very effective, but imposed a handicap upon the Committee because 
it had been customary to obtain only one copy of each author's 
manuscript, and occasionally it was necessary for both Committee 
Chairmen to refer to a manuscript simultaneously. 

Accordingly, it was decided that our request for manuscripts before 
the meeting should specify two copies so that the Publicity Committee 
could have the exclusive use of one set. It is always possible, of 
course, for an author to make the reservation, when turning in his 
copies, that further corrections may be necessary on the manuscript 
and that the Committee is not to release the copy submitted, for 
publication in the JOURNAL, until these corrections are supplied. 
If the manuscript is essentially correct (even though some or all of 
the figures may be missing), it is usually satisfactory for publicity 

A request for a finished manuscript 10 days before the meeting is 
not believed to be too severe, and past experience has shown that the 
majority of authors are able to meet these requirements satisfactorily. 

It may be of interest, in conclusion, to present a rough classification 
of the information that has been presented to the membership at our 
last four meetings. Your comments and suggestions are requested. 
The number and type of papers may be divided broadly as follows : 

Acoustics 4 Optics 

Apparatus 28 Lighting [ 34 

Color 9 Projection J 

Education ] Sound 30 

Historical > 11 Stereoscopy 1 

Industrial j Stereophony J 

General Engineering Practice 8 Television 3 

Laboratory } 2g 
Photographic J 

This summary indicates that emphasis has been placed about 
equally on papers dealing with apparatus, laboratory and photo- 
graphic problems, optics, lighting, and projection. The papers on 
sound have dealt with many aspects of this subject, and the total 


number of papers in the class is about the same as the total in each of 
the other classes. These figures show that no single subject of these 
fundamental classes has been emphasized at our meetings to the ex- 
clusion of others. 

The usual effort has been made to obtain papers for the 1938 spring 
meeting. The results have been most encouraging. Approximately 
69 papers have been offered and only 3 were withdrawn. There are 
15 papers scheduled on the program, the authors of which will not be 
present. These will be restricted to 10 minutes or may be read by 
title if time is limited. There are 15 papers dealing with apparatus 
and these are limited to 10 minutes for presentation. A total of 36 
papers remain, therefore, for which a longer reading time has been 

It is particularly gratifying to note the number of papers on the 
program by technicians on the West Coast, and the Committee wishes 
to acknowledge the excellent cooperation shown by the Research 
Council of the Academy of Motion Picture Arts & Sciences in con- 
nection with the preparation of the program. 

The generous response to our request for papers indicates that we 
may yet achieve the goal of every technical society a selected papers 
program and a large enough volume of paper material to permit the 
editorial board to publish a selected group of high-quality papers in 
each number of our JOURNAL. 

G. E. MATTHEWS, Chairman 





(West Coast) 

L. A. AICHOLTZ, Chairman 





This bulletin contains details regarding the preparation of material for papers, 
both for presentation and for publication, and also includes information on the 
Administrative Practices of this Society relative to the responsibility it assumes 
regarding the acceptance of papers for publication. Please read the information 


Sect. 8, Div. 4 Administrative Practices reads as follows: 

Instructions to Authors. Papers may be submitted for presentation at the Semi- 
Annual Conventions, for publication in the JOURNAL of the Society without presen- 
tation at Conventions, or for presentation at Local Section meetings. 

Papers will not be accepted for presentation at Semi-Annual Conventions unless 
their quality is regarded by the Board of Editors to be such as to merit publication 
In many cases, however, it is impossible for the authors to submit manuscripts 
sufficiently in advance of a Semi-Annual Convention to permit careful examination 
by the Board of Editors. The Board of Editors, therefore, shall reserve the right 
to decline to publish any paper not submitted at least one month prior to a Semi- 
Annual Convention and approved, even though it be accepted by the Papers Com- 
mittee of the Society and presented at a Semi-Annual Convention. Papers 
presented at Local Section meetings are subject to these same regulations. 

Papers accepted for publication but not presented at Conventions or other 
Society meetings will be published as early as possible, but do not have priority 
over those already in the hands of the Editorial Staff. 

The subject matter of papers should be such as to be of interest to the motion 
picture engineer, the term "engineer" being regarded in a very broad sense as 
"anyone who contributes to the building of the motion picture." 

Prior Right of Publication. Papers presented at Conventions or other meetings 
of the Society or submitted only for publication in the JOURNAL shall be regarded 
as the confidential property of the Society unless withdrawn by the author, and 
shall not be published elsewhere (except upon the approval of the Editorial Vice- 
President) until they have either been published in the JOURNAL or have been 
returned to the author. Prior publication to the extent of 30 per cent of the ver- 
bal length of any paper, with due acknowledgment of the source, is permitted. 

Right to Reprint. After its date of appearance in the JOURNAL, an article may 
be published in other publications provided complete credit is given to the JOUR- 
NAL of the Society of Motion Picture Engineers and to the author of the article in 
question. The citation should appear preferably after the title of the article or 
as a footnote to the article on the first page and should read as follows: Re- 
printed from Journal of the Society of Motion Picture Engineers, Volume, Page, 
Month, Year. 

Prior Publicity of Convention Papers. Publicity incident to the presentation of 
papers at conventions is the responsibility of the Papers and Publicity Committees 
of the Society and should not be undertaken by the authors or their representa- 
tives, except in collaboration with these Committees. 

An abstract or abridgment for publicity purposes about 200 words long should 
be supplied about six weeks before the meeting at which the paper is to be read. 
Examples of satisfactory abstracts are the following: 

"High-Speed Motion Picture Photography Applied to Design of Telephone 
Apparatus"; W. Herriott, Bell Telephone Laboratories, Inc., New York, N. Y. 

High-speed motion pictures are employed at Bell Telephone Laboratories as a 
visual aid in the study of problems associated with the design, manufacture, and 
testing of telephone apparatus. A new high-speed camera of the optical compen- 
sator type operating at 4000 pictures per second is described, and its application 
to the study of problems associated with telephone apparatus is discussed. 


"A Modern Motion Picture Laboratory"; C. L. Lootens, Republic Productions, 
Inc., North Hollywood, Calif. 

A complete description of the new laboratory of the Consolidated Film Indus- 
tries, Inc., which was completed during the winter 1936-37. Included are layouts 
and pictures of equipment in the basement, first, and second floors. The de- 
scription of the laboratory and equipment follows the sequence of operation of 
negative development, "dailies," master and release printing, together with a 
description of the special printers, processing units, chemical system, silver re- 
covery system, and other mechanical items of interest. 

"Reduction of Loop-Length Variations in Non-Slip Printers"; E. W. Kellogg, 
RCA Manufacturing Co., Inc., Camden, N. J. 

Compensation for varying degrees of film shrinkage is accomplished in the 
Bedford non-slip printer by changes in the length of a loop of film between a 
sprocket and the printing point. This involves uncertainty of synchronism by 
the amount that the loop, as first threaded, differs in length from the final running 
loop. For most purposes, the present designs do not cause more change in loop- 
length than may readily be tolerated. 

For certain purposes, especially if this type of printer is to be employed for 16- 
mm. films, there may be too much departure for synchronism. A guide-roller 
arrangement is described by which the necessary change of angle of approach of 
the raw stock to the printing point is attained with comparatively small change 
in loop-length. 

Several possible arrangements are considered and some other features of the 
non-slip printer are discussed. 

Order of Publication. The order of publication of material presented at con- 
ventions or submitted only for publication in the JOURNAL is at the discretion of 
the Board of Editors and is determined in general by the chronological order in 
which the papers are received, the timeliness of the material, the technical quality 
of the papers, and their editorial completeness. The Board of Editors will give 
due and proper consideration to requests for special and early publication. 

The Complete Manuscript. The complete manuscript, from the editorial point 
of view, consists of the following items: 

(a) Title. 

(6) Name of author. 

(c) Company affiliation (as a footnote on the first page). 

(d) Summary of paper (not to exceed 500 words). 

(e) The paper proper. 

(/) A complete list of references or citations. 

(g) A complete set of illustrations suitable for making engravings, with a cap- 
tion for each illustration. 

Text. Papers should be typewritten, double spaced, upon only one side of the 
paper. It is desirable to send for publication the original (ribbon copy) a car- 
bon copy is easily erased and may become illegible. 

Illustrations. Each drawing or photograph should occupy a separate sheet 
and be capable of good reproduction. Blueprints, photostats, or sepia prints will 
not be accepted. Tracings or line-drawings should be made with black india ink 



[J. S. M. P. E. 

upon white paper or tracing cloth. Closely spaced coordinate lines on curves 
should be avoided. 

The minimum amount of reading matter should be included upon the illustra- 
tions. Necessary information can better be set in type in the caption accompany- 
ing the illustration. 

The maximum width of a JOURNAL cut is 4 inches and the maximum height is 
6V4 inches. Illustrations or drawings should preferably be larger and not smaller 
than these size requirements. It is important that the necessary reduction of an 
illustration will not make the height of letters contained in reading matter on the 



FIG. 1. Good example of a drawing. 

illustration less than l / 32 inch. All inscriptions on graphs or illustrations should be 
lettered and not typewritten. 

When preparing illustrations, the style of lettering should be so chosen and the 
lettering so placed upon the illustrations as to be easily read when projected as 
lantern-slides before an audience of several hundred persons. Slides are usually 
reproduced about ten or more feet wide, and should be readable at a distance of 
fifty feet. Examples of satisfactory illustrations are shown in Figs. 1 and 2. 

Listing Captions. Captions for figures and tables should be listed upon sepa- 
rate sheets accompanying the manuscript. 

Aug., 1938] 



Address. It is important that the author's business affiliation and mailing 
address be written upon the first page of the manuscript. 


The value and clarity of a paper are undoubtedly increased by dividing it into 
sections. The author can assist the editorial office by specifying the type of 
heading or sub -heading desired in each instance. The headings conforming 
to JOURNAL style, in descending order of importance, are as follows. 

.3 .4 .5 A .8 1.0 2 


3 456 8 10 

FIG. 2. Good example of a graph. 


Italic Centerhead 
Italic Sidehead. These sideheads are run into the text of the paragraph. 


References to literature should be accurate and complete. References 
periodical literature should contain the following items in the given order: 


(1) The reference number, corresponding to the number in the text. 

(2) The name of the author of the paper; correctly spelled and with initials. 
(5) The name of the article, in quotation marks. 

(4) The name of the periodical (unless the periodical is well known its title 

should not be abbreviated). 

(5) The volume number. 

(6) The date, month, and year, in parentheses. 


(7) The serial number, preceded by the abbreviation "No." 

(8) The page number, preceded by the letter "p." 

Example: l McCov, J. L.: "A Light-Intensity Meter," /. Soc. Mot. Pict. 
Eng., XIV (March, 1930), No. 3, p. 357. 

Reference to books should be made as follows: 

(1} Author's name. 

(2) Name of book, in quotation marks. 

(5) Edition. 

(4) Publisher. 

(5) Place of publication. 

(6) Date of publication, in parentheses. 

(7) Page, preceded by letter "p." 

Example: FRANKLIN, H. B.: "Sound Motion Pictures." 1st Ed. Doubleday, 
Doran & Co., Garden City, L. I., N. Y. (1929), p. 101. 

Reprints. Reprints of articles published in the JOURNAL may be obtained from 
the Society's headquarters office, Pennsylvania Hotel, New York, N. Y. These 
reprints are most economically obtainable currently with the publication of the 
issue of the JOURNAL in which they appear. Prices in the quantity desired may 
be obtained by communicating with the Society's headquarters office. 


(2) Two copies of each manuscript must be delivered to the Chairman of the 
Papers Committee at least one month before the meeting date in order that the 
paper be presented at the meeting. Papers arriving less than one month before 
the meeting date may, at the discretion of the Papers Committee, be scheduled on 
the program to be read by title or substituted for other papers in the event of 

(2) Two copies are needed in order that one set may be made available for the 
Publicity Committee and one for the Papers Committee during the period of the 

(3) Final and complete copies ready for publication are desired. In the event 
that such are not possible, preliminary copies requiring further slight alterations 
in text or completion of illustrations (as per regulations regarding preparation for 
publication) before final release by the author will be accepted. These changes 
should be made, however, within one week after the meeting. 

(4) Authors are urged to study carefully the regulations on the preparation of 
illustrations, and to give consideration to the legibility of the figures (I) as lan- 
tern-slides when the paper is read at the meeting, and (2) as printed cuts in the 


The attention of all authors is directed especially to the following sugges- 
tions regarding oral delivery of their papers at Conventions. Valuable time of 
the delegates and other authors will be conserved if each author on the program 
follows these suggestions: 


(1) Arrangement of Material. Manuscripts prepared for publication are 
seldom suitable for oral presentation. The paper should convey clearly to the 
hearer: (a) the purpose of the work; (6) the experimental method; (c) the re- 
sults obtained; and (d) conclusions. The nature of the material and the time 
available for presentation will determine the degree of emphasis to be placed 
upon each subdivision. The author should make certain by trial against his 
watch that the essential points can be presented adequately in the time allotted 
to the paper. 

(2) Statement of Purpose. Orient the audience clearly as to the nature and 
purpose of the work. A lengthy historical review is generally out of place. 

(3} Technic. Describe the experimental method employed so as to indicate 
the principles involved. Omit details of apparatus or procedure unless there is 
some particularly novel development. Such data may belong in the published 
paper but will bore your audience. 

(4) Statement of Results. Present the results graphically, preferably with dia- 
grams. Lantern-slides are more clearly seen than hand-drawn charts. These 
slides should be of standard size (3.25 X 4 inches) and should project clearly on 
the screen. Lettering should be kept to a minimum, consistent with clarity, and 
should be of such size that when the illustration is reduced for publication in the 
JOURNAL, the reduced lettering will not be smaller than 1 / 32 inch in height. 
Usually it is not satisfactory to typewrite legends on drawings, especially if the 
typewriter type is small. Regardless of who has made the charts or slides, try 
them from the point of view of the audience before presenting them at the meet- 
ing. Do not read tables, a procedure that wastes time and destroys interest, 
but point out the general trend of the data. Whenever possible, the results of 
research should be shown by means of motion pictures, for which adequate pro- 
jection facilities will be available. 

(5) Conclusions. Summarize the evidence and discuss the importance of the 
results or conclusions to the particular field of research involved. 

(6} Manner of Presentation. Do not read from a manuscript verbatim, unless 
the material has been written expressly for oral presentation. Talk directly to 
your audience in a clear, loud voice. Do not face blackboard or screen while 
speaking. Articulate distinctly. 

(7) Demonstrations. Details of demonstrations should be checked carefully 
before the opening of the session during which the demonstration is to be given. 
This will insure a smoother demonstration and avoid using up valuable time during 
the technical session. 

Many exceptions to, and modifications of, the above suggestions will apply in 
particular instances. Nevertheless, general adherence to the points brought out 
will go far toward eliminating the valid criticisms that have been aimed at our 

Acknowledgment is made to the Society of American Bacteriologists and the 
American Chemical Society for many of the ideas incorporated in these sugges- 



The editors present for convenient reference a list of articles dealing with subjects 
cognate to motion picture engineering published in a number of selected journals. 
Photostatic copies may be obtained from the Library of Congress, Washington, D. C., 
or from the New York Public Library, New York, N. Y. Micro copies of articles 
in magazines that are available may be obtained from the Bibliofilm Service, Depart- 
ment of Agriculture, Washington, D. C. 


18 (May, 1938), No. 5 

Home Newspapers by Radio (pp. 7-9, 35) F. C. EHLERT 

General-Purpose Audio Amplifier (pp. 1 1-13, 26, 30) A. PREISMAN 
Measuring the Recording System with Limited Equip- 
ment (pp. 14-15, 36-37) A. W. NIEMANN 


11 (May, 1938), No. 5 

Wideband Television Amplifiers II (pp. 24-27) 
Reverberation Control in Broadcasting (pp. 28-29) H. A. CHINN 
A Method of Periodical Sound Reproduction (pp. 38, 40) T. KORN 
Multiplying the Range of the Vacuum Tube Voltmeter 

(pp. 42, 44, 46) G. R. CHINSKI 

Theater Sound Reproducing System Standards (pp. 46, 

48, 50) J. K. HILLIARD 

International Photographer 

10 (May, 1938), No. 4 

Tradewinds News of New Products (pp. 5-8) 
Electrometric Titration Method (pp. 22-24) D. K. ALLISON 

International Projectionist 

13 (May, 1938), No. 5 
The Geneva Intermittent Movement : Its Construction 

and Action. Ill (pp. 7-11) A. C. SCHROEDER 

Notes on Audio Amplification (pp. 12, 15-16) L. P. WORK 

Measuring Projected Light and Screen Brilliancy (pp. 

17-19) J. A. COOK 

Analyses of Modern Theater Sound Reproducing Units 

(pp. 20-23, 32) A. NADELL 

Enlarging the Visual Field of the Motion Picture (pp. 

24-25, 31, 32) R. SCHLANGER 

A New Arc Aligning Method : The Bantau "Theaomai" 

(pp. 26-27, 30-31) K. NUNAN 





20 (May, 1938), No. 5 
Zur Theorie des Rauschens (Ground-Noise Theory) 

(pp. 116-118) 
Das Farbfilmverfahren von Prof. Roux (Prof. Roux's 

Color-Film Process) (p. 119) 
Das Problem des plastischen Tones im Film (Problem 

of Stereoscopic. Effects on Film) (pp. 120-125) 
Bemerkungen zur Anwendung des Raumton-Effektes 

im Tonnlm (Remarks on the Use of Stereo-Sound 

Effects on Sound-Film) (pp. 125-126) 

Photographische Industrie 

36 (May 4, 1938), No. 18 

Neue Tonfilm-Kamera fur 16-Mm. Schmalfilm (New 
16-Mm. Sound Camera) (p. 537) 

36 (May 25, 1938), No. 21 

Die optischen Grundlagen fur die Form des Linsenras- 
terfilms in der Farbenphotographie (Optical Basis 
for the Form of Lenticular Screens for Color Photog- 
raphy) (pp. 610-612) 

Proceedings of the Institute of Radio Engineers 

26 (May, 1938), No. 5 
The Fine Structure of Television Images (pp. 540-575) 









Officers and Committees in Charge 

W. C. KUNZMANN, Convention Vice-President 
J. I. CRABTREB, Editorial Vice-P resident 
G. E. MATTHEWS, Chairman, Papers Committee 
H. GRIFFIN, Chairman, Projection Committee 
E. R. GEIB, Chairman, Membership Committee 
J. HABER, Chairman, Publicity Committee 




Local Arrangements 

K. BRENKERT, Chairman 




Registration and Information 

W. C. KUNZMANN, Chairman 



Hotel and Transportation Committee 

A. J. BRADFORD, Chairman 






H. GRIFFIN, Chairman 






Officers and Members of Detroit Projectionists Local No. 199 



J. F. STRICKLER, Chairman 




J. HABER, Chairman 



Ladies' Reception Committee 

MRS. J. F. STRICKLER, Hostess 

assisted by 





The Headquarters of the Convention will be at the Hotel Statler, where excellent 
accommodations are assured. A reception suite will be provided for the Ladies' 
Committee, who are now engaged in preparing an excellent program of entertain- 
ment for the ladies attending the Convention. 

Special hotel rates guaranteed to SMPE delegates and friends, European plan, 
will be as follows: 

One person, room and bath $3.00 to $6.00 

Two persons, room jand bath 5.00 to 8.00 

Two persons (twin beds), room and bath 5.50 to 9.00 

Three persons, room and bath 7.50 to 10.50 

Parlor suite and bath, for one 8.50 to 11.00 

Parlor suite and bath, for two 12.00 to 14.00 

Room reservation cards will be mailed to the membership of the Society in the 
near future, and everyone who plans to attend the Convention should return his 
card to the Hotel promptly in order to be assured of satisfactory accommodations. 
Registrations will be made in the order in which the cards are received. Local 
railroad ticket agents should be consulted as regards train schedules, and rates to 
Detroit and return. 

The following special rates have been arranged for SMPE delegates who motor 
to the Convention, at the National-Detroit Fireproof Garage (the Hotel Statler's 
official garage), Clifford and Elizabeth Streets, Detroit: Self -delivery and pick-up, 
12 hours, $0.60; 24 hours, $1.00; Hotel-delivery and pick-up, 24 hours, $1.25. 
Special weekly rates will be available. 

Technical Sessions 

An attractive and interesting program of technical papers and presentations is 
being assembled by the Papers Committee. All technical sessions, apparatus 
symposiums, and film programs will be held in the Large Banquet Room of the 

Registration and Information 

Registration headquarters will be located at the entrance of the Large Banquet 
Room, where members of the Society and guests are expected to register and re- 
ceive their badges and identification cards for admittance to the sessions and film 


programs. These cards will be honored also at several motion picture theaters 
in the neighborhood of the Hotel, during the days of the Convention. 

Informal Luncheon and Semi-Annual Banquet 

The usual Informal Luncheon will be held at noon of the opening day of the 
Convention, October 31st, in the Michigan Room of the Hotel. On the evening of 
Wednesday, November 2nd, the Semi- Annual Banquet of the Society will be held 
in the Grand Ballroom of the Hotel at 8 P.M. Addresses will be delivered by 
prominent members of the industry, followed by dancing and other entertainment. 

Points of Interest 

In addition to being a great industrial center, Detroit is also well known for the 
beauty of its parkways and buildings, and its many artistic and cultural activities. 
Among the important buildings that one may well visit are the Detroit Institute 
of Arts; the Detroit Historical Society Museum; the Russell A. Alger House, a 
branch of the Detroit Institute of Arts; the Cranbrook Institutions; the Shrine 
of the Little Flower; and the Penobscot Building. 

At Greenfield Village, Dearborn, are grouped hundreds of interesting relics of 
early American life, and there also is located the Edison Institute, established by 
Henry Ford in memory of Thomas A. Edison. 

On the way to Greenfield Village is the Ford Rotunda, a reception hall for visi- 
tors to the Ford Rouge Plant. Here are complete reproductions and displays of 
motorcar design, and representations of the famous highways of the world, from 
Roman days to modern, are on the grounds surrounding the building. 

The General Motors Research Building and Laboratory, located on Milwaukee 
Avenue, will be of particular interest to engineers visiting the City. 

Various trips may be taken from Detroit as a center to Canada, by either the 
Ambassador Bridge or the Fleetway Tunnel; to Bloomfield Hills, a region of 
lakes; Canadian Lake Erie trip from Windsor, Ontario; to Flint, Michigan, 
another center of the automotive industry; to Milford, General Motors' Proving 
Grounds; and to the Thumb of Michigan Resort Beaches. The City contains 
also a number of beautiful parks and golf courses. 



At a meeting of the Committee held on July 8th, the question of film cores was 
considered and tentative dimensions were proposed by Mr. P. Arnold, Chairman 
of the Sub-Committee dealing with the subject. Drawings are being prepared 
and a ballot of the Standards Committee will be taken very shortly. 

Further study was given to the question of 35-mm. sound-track dimensions 
by the Sub-Committee under the Chairmanship of L. W. Davee, and J. A. Maurer 
reported for his Committee on Optical Reduction Ratio that a definite report 
and recommendation will be forthcoming at the next meeting, as soon as opinions 
have been received from all manufacturers and laboratories concerned with re- 
duction printing. 

The specifications for safety-film proposed by the French Standards Association 
for the meeting of Committee 36 of the ISA at Berlin during July were considered 
by the Committee. Final action on these specifications will be taken in the near 
future, as soon as the opinions of the Underwriters Laboratories have been ob- 


The last meeting of the season was held on June 23rd at the Paramount Build- 
ing, New York, under the Chairmanship of Harry Rubin. Unfinished business 
was completed and preparations made for resuming the activities of the Committee 
in the fall, the date of the next meeting being scheduled for September 15th. In 
the meantime, several meetings of the Sub-Committees on Projection Room Plans, 
under the Chairmanship of S. Harris, and on Projector Tools and Tolerances, 
under the Chairmanship of P. Larsen, have been held, and it is expected that com- 
plete reports will be available from these Sub-Committees by the end of the 

The proposed revision of the NFPA "Regulations for Handling Nitrocellulose 
Film" has been completed and copies of the revision have been transmitted to a 
special committee established by the NFPA to consider it. It is expected that 
the revision will be in proper shape for publication in the fall. The SMPE is 
represented on the NFPA Committee by S. Harris, Chairman of the Sub-Com- 
mittee on Projection Room Fire Regulations, of the Projection Practice Com- 


At a meeting of the Pacific Coast Section held at the Filmarte Theater in Holly- 
wood on June 29th, two papers presented at the Washington Convention last 
May were re-presented, namely, "The Transmission of Motion Pictures over a 
Coaxial Cable," by H. E. Ives of the Bell Telephone Laboratories; and "The In- 



fluence of />H on Washing Films after Processing," by S. E. Sheppard and R. C. 
Houck of the Eastman Kodak Company, Rochester. The former paper was] 
presented by L. F. Brown of Electrical Research Products, Inc., and the latter byl 
R. B. Atkinson. A resume of the proceedings of the Washington Convention was 
presented by J. G. Frayne. 



In the June, 1938 issue of the JOURNAL, beginning on page 656, appeared the 
above-entitled article by John K. Hilliard, describing the Academy Standard 
sound-track nomenclature approved by the Research Council of the Academy 
of Motion Picture Arts and Sciences and published in the Academy Research 
Council Technical Bulletin of November 24, 1937. 

As reprinted in the JOURNAL, the article employed the term "variable-width" 
throughout, instead of the term "variable-area" as approved by the Research 
Council in the original publication. 

The entire Standard Nomenclature is now under consideration by the Sec- 
tional Committee on Motion Pictures of the American Standards Association, 
and if adopted these terms will hereafter be used throughout the industry to 
designate the various indicated types of sound-track. 

In particular, the term "variable-area" has been approved by the studios and 
by the equipment companies involved to designate that type track, throughout 
the industry. 

Readers of the JOURNAL should, therefore, in the above-mentioned article sub- 
stitute the term "variable-area" whenever designating that type of track, instead 
of the term "variable- width." 




Volume XXXI SEPTEMBER, 1938 Number 3 



A Water-Cooled Quartz Mercury Arc 


Negative-Positive Technic with the Dufaycolor Process 

T. T. BAKER 240 

Application of Non-Linear Volume Characteristics to Dialog 
Recording J. O. AALBERG AND J. G. STEWART 248 

The Transmission of Motion Pictures over a Coaxial Cable. . 


Maintenance of a Developer by Continuous Replenishment. . 

R. M. EVANS 273 

Sound-Stages and Their Relation to Air-Conditioning 


New Motion Picture Apparatus 

Problems in the Use of Ultra-Speed Negative Film 

P. H. ARNOLD 307 

Permanent-Magnet Four-Ribbon Light- Valve for Portable 
Push-Pull Recording E. C. MANDERFELD 315 

A Basically New Framing Device for 35-Mm. Projectors . . . 

H. A. DEVRY 319 

Current Literature 322 

Book Review 324 

Detroit Convention . . 325 





Board of Editors 
J. I. CRABTREE, Chairman 



Subscription to non-members, $8.00 per annum ; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscriptions or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 
Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 

West-Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1938, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is 
not responsible for statements made by authors. 


"President: S. K. WOLF, RKO Building, Rockefeller Center, New York, N. Y. 
"Past-President: H. G. TASKER, Universal City, Calif. 
"Executive Vice-P resident: K. F. MORGAN, 6601 Romaine St., Los Angeles, 


""Engineering Vice-President: L. A. JONES, Kodak Park, Rochester, N. Y. 
*Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 
** Financial Vice-President: E. A. WILLIFORD, 30 E. 42nd St., New York, N. Y. 
* Convention Vice-President: W. C. KUNZMANN, Box 6087, Cleveland, Ohio. 
"Secretary: J. FRANK, JR., 90 Gold St., New York, N. Y. 
"Treasurer: L. W. DAVEE, 250 W. 57th St., New York, N. Y. 


*J. O. AALBERG, 157 S. Martel St., Los Angeles, Calif. 

*M. C. BATSEL, Front and Market Sts., Camden, N. J. 

**R. E. FARNHAM, Nela Park, Cleveland, Ohio. 

*G. FRIEDL, JR., 90 Gold St., New York N. Y. 

*A. N. GOLDSMITH, 444 Madison Ave., New York, N. Y. 

**H. GRIFFIN, 90 Gold St., New York, N. Y. 

**A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

*S. A. LUKES. 6145 Glenwood Ave.. Chicago, 111. 

*Term expires December 31, 1938. 

**Term expires December 31, 1939. 


Summary. The structure of the water-cooled quartz mercury lamp, its operation, 
quality of radiation, brightness, and source size limitations are first described, followed 
by a discussion of the power-supply equipment, both a-c. and d-c. Applications oj 
the lamp are as follows: 

(1) Motion picture projection, with single lamps and with several sources. 

(2) Motion picture photography, both black-and-white and color, and the ap 
plication to very high-speed motion picture photography. For black-and-white photog 
raphy the lamp is quite satisfactory. For color work the relatively limited red radia 
tion may call for external methods, either in the use of fluorescent reflectors or a highly 
red-sensitive emulsion, to make up for this deficiency. 

(3} Film printing. Because of the relatively high output in the blue-violet and 
ultraviolet regions this lamp may prove a very satisfactory source, especially where 
advantage is taken of the ultraviolet radiation. 

The following additional applications, of secondary interest to the motion picture 
industry, are also discussed: photo-enlarging, photoengraving, and searchlights. 

Within the past few years a number of new mercury-vapor light- 
sources have made their appearance. 1 New materals and technics 
have made possible operation at temperatures and pressures far 
above previous values and at which the characteristics of the light 
emitted differ greatly from those of the older type of mercury source 
It is the purpose of this paper to discuss the work done at Nela Park 
on one of the newest developments a water-cooled quartz mercury 
lamp operating at a pressure of about 1100 pounds per square-inch 
and some of its possible applications in the motion picture industry 

Construction of the Lamp. A 1000-watt lamp of this type is shown 
in Fig. 104). It consists of a quartz tube about 40 mm. long having 
an outside diameter of 6 mm. and a bore of 2 mm. Sealed into each 
end by means of a special glass are tungsten wires which are both the 
leads and the electrodes. The tips of the wires project just through 
the surface of a small quantity of mercury located in each end of the 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 20, 1938. 

** General Electric Co., Cleveland, Ohio. 


222 E. B. NOEL AND R. E. FARNHAM [J. S. M. P. E. 

lamp. In order to aid in starting, the lamp is filled with argon gas 
at 50 mm. pressure. Other characteristics are listed in Table I. 

When not lighted, the internal pressure is that of the argon gas, 
namely, Vi& of an atmosphere. However, when lighted, the heat 
from the arc vaporizes some of the mercury in the pools around the 
electrodes, building up a pressure of the order of 75 atmospheres, the 
exact value being determined by the wattage input and the distance 
by which the electrodes project from the surfaces of the mercury. 


Characteristics of 1000- Watt Water- Cooled Quartz Mercury Lamp 

Arc Length 25 mm. 

Inside Diameter 2 mm. 

Outside Diameter 6 mm. 

Operating Pressure 75 atm. 

Watts 1000 

Operating Volts 840 

Operating Amperes (a-c.) 1.4 

Lumens per Watt 65 

Lumens 65,000 

Max. Surface Brightness (initial) 30,000 candles/cm 2 . 

Burning Position Horizontal 

In order to be able to dissipate 1000 watts within such a small 
volume the lamp must be cooled very effectively. It is not sufficient 
merely to place the lamp in a bath of water; the water must be passed 
over the lamp with enough velocity to prevent the formation of 
steam bubbles on the surface of the quartz. Placed around the lamp 
is a "velocity tube" having a radial clearance from the lamp of about 
1 mm., through which the water must flow. Because of this restricted 
cross-section, more than ample water velocity is attained to prevent 
the formation of steam with a water flow of about three liters per 
minute. In passing over the lamp the increase in water temperature 
is only a few degrees Centigrade. 

One type of cooling jacket is shown in Fig. 1(B). Water enters at 
one end and leaves at the other, while electrical connections are made 
at each end of the jacket on the brass rings. A socket for this type 
of jacket is shown in Fig. 2, while Fig. 3 shows one designed to take 
two such lamps. 

Since both leads to the lamp are in contact with the water, the arc 
operates in parallel with a water resistance. Where the water sur- 
rounding the lamp has a large cross-section the resistance is low 



enough to interfere with the operation of the lamp. With a "velocity 
tube" around the lamp, however, the cross-section of the water is 
small enough so that the current through the water is only 10 to 25 

Spectral Distribution of the Discharge. Incandescent sources, such 
as tungsten and the crater of a carbon arc, emit a continuous spec- 
trum; that is, all colors of light are given out. Luminous vapors 
and gases, however, emit only certain 
colors which are characteristic of the 
substance. Fig. 4 shows the spectra of 
a number of commercial mercury- vapor 
sources and the spectra of a water- 
cooled quartz mercury lamp operating 
at various pressures. The spectrum of 
the Cooper-Hewitt lamp operating at 
0.0003 atmosphere shows only a few 
distinct lines. That of the H-l operat- 
ing at 1.4 atmospheres appears to be 
little different. The H-4 lamp spec- 
trum at 8 atmospheres shows the pres- 
ence of a very weak "background 
radiation" the colors between the 
mercury lines are beginning to fill in. 
At 25 atmospheres (the H-3 lamp), the 
background is somewhat stronger; and, 
in addition, it will be noticed that the 
main spectral lines are no longer sharp, 
the blurring being more pronounced on 
the long-wave side. 

With the water-cooled lamp the cur- 
rent densities and pressures are so 
much greater that the lines are even 
more blurred and the continuous back- 

U) W 

FIG. 1. 1000-watt water- 
cooled quartz mercury lamp: 
04) the lamp proper; (B) 
the lamp in place in its water 

ground forms a very appreciable portion of the radiation.* The 
spectral distribution curves of Figs. 5 and 6 may show this even 
better. At the highest loading, shown in Fig. 6(D), the lamp life 
is quite short, but if a better material than quartz becomes available 
lamps operating at this pressure may be practicable.** The emitted 

* Pressures are calculated from the formula 2 P a tm 
** Cf. footnote p. 9. 

(Gradient - 100)/3. 



[J. S. M. P. E 

light contains appreciable red, as shown by Table II. 4 The effect of 
this upon the rendition of skin tones is quite noticeable. 

As the pressure is increased still further, the lines merge more and 
more into the background until they disappear completely. Mr. 
Cornelias Bol, who did the original work on these lamps at The Philips 
Co. in Holland, and who is now associated with our Company, has 

FIG. 2. Single-unit socket with lamp 
and jacket in position. 

FIG. 3. Socket for two lamps. The 
cap is hollow, to allow the water to 
flow up through one lamp and down 
through the other. 

been experimenting with mercury discharges at extremely high pres- 
sures at Stanford University. By enclosing a lamp in a bomb-like 
vessel and subjecting it to an external pressure of 10,000 pounds per 
square-inch to prevent it from bursting he obtained the spectrogram 
of Fig. 7, which at the highest voltage per centimeter and pressure 
shows complete absence of lines. It shows also that as the pressure is 
increased, there is less and less short-wave ultraviolet emitted. 



2 Q 

4J LO |> 

J0 ^H ^^ 

CO (M 

^O CO 

"-O 00 TH O 



I- - 

w O O O 

TS O O ^f 

O T-l Oi b- 


fiq O 


E. B. NOEL AND R. E. FARNHAM [j. s. M. p. E. 

FIG. 5. Spectral energy distribution curves 
for water-cooled lamp (top) and two air-cooled 
lamps (below). The ordinates are milliwatts 
per 100 Angstrom units per steradian per watt 







7000 4 8000 





FIG. 6. Spectral energy distribution curves for a water-cooled 
quartz mercury lamp operating at different pressures. The ordi- 
nates are milliwatts per 100 Angstrom units per steradian per watt 



The alteration in the spectral distribution as the pressure is in- 
creased is such that the color of the light is materially changed. In 
air-cooled lamps at very low pressures the discharge is distinctly 
greenish, but as the pressure is raised, the color becomes more and 
more white. These changes are plotted in Fig. 8 on the standard 
I.C.I, color-chart. On this chart the points for pure spectral colors 
lie on the large boundary curve as marked, while those for unsatu- 
rated colors lie inside. The dominant hue is determined by the direc- 



FIG. 7. Spectrogram by C. Bol at Stanford University: quartz mercury arc 
with gap of 10 mm. and bore of 1 mm. operating in steel container with the circu- 
lating water under a pressure of 10,000 Ibs. per square-inch. 

tion, and the saturation by the distance from the daylight point. It 
may be seen, as the pressure of mercury is increased in the series of 
lamps tested, that while the hue changes from green to yellow-green 


Percentage of Total Light from Mercury Arcs Operating at Various Pressures, from 
Sun, from a Tungsten Lamp, of Wavelength 6000-7600 A 



H-l Lamp 

H-4 Lamp 

H-3 Lamp 

Water-Cooled Capillary 'Arc 


500- Watt, 11 5- Volt Tungsten 




Per Cent 

of Light 





to blue, the light actually becomes very nearly white as shown by 
the closeness with which the points for high-pressure operation ap- 
proach the daylight point. 

Brightness of the Discharge. Even more unique than the fact that 
these lamps have appreciable continuous radiation is their intrinsic 
brightness. Fig. 9 shows the brightness of water-cooled lamps oper- 


E. B. NOEL AND R. E. FARNHAM [j. s. M. p. E. 

1931 i.c.i. SYSTEM- 

FIG. 8. Color coordinates of mercury lamps operating 
at various pressures. 



SS OF 2 

VM. I.D. 


I 40000 



















> M 


Ss " 



FIG. 9. Maximum brightness of water-cooled mer- 
cury arcs operating at various pressures in tubes of 
2-mm. inside diameter. 


ated at various pressures.* These figures should be compared with 
the brightness of a 1000- watt projection lamp, which is 3100 candles 
per square-centimeter and that of a crater of a carbon arc, which 
ranges from 14,000 candles per square-centimeter for the regular 
type to 50,000 to 86,000 candles per square-centimeter for the high- 
intensity type. The brightness of the quartz lamp is essentially 
constant along the length of the arc, but across the arc stream it 
varies as shown in Fig. 10. Since it is a line source of light, for some 
applications, several must be used side by side, or the more usual 
type of optical systems must be modified for use with a source of this 


Comparison of Energy Radiated in the Ultraviolet, Visible, and Infrared Portions of 

the Spectrum by a 1000-Watt Quartz Water-Cooled Mercury Lamp and a 1000- 

Watt High-Efficiency Biplane- Filament Lamp. (For the Tungsten Lamp the Figures 

Are for Energy Radiated beyond the Bulb by the Filament) 

1000-Watt 1000-Watt 

Biplane Water-Cooled 

at 27.5 LPW Mercury 

Ultraviolet (3000-4000 A) 5 watts 20 watts 

Visible (4000-7600 A) 145 watts 284 watts 

Infrared (7600-14,000 A) 690 watts 76 watts 

Total watts radiated 840 380 

Lumens 27,500 lumens 65,000 lumens 

Coolness of the Light. One of the most valuable characteristics of 
the lamp is the coolness of its light. This is illustrated in Table III, 
where a 1000- watt quartz lamp is compared with a high-efficiency 
biplane lamp. It will be seen that for equal lamp wattage the 
quartz lamp radiates more than 2 1 /* times the light but only 45 per 
cent of the energy of the tungsten lamp. Thus, to supply an equal 
amount of light, only 42 per cent as much wattage is required in a 
water-cooled quartz lamp as with the tungsten-filament source, and 
the radiated energy is reduced to one-fifth. If the comparison were to 
be made on the basis of photographic effectiveness, the result would be 
even more favorable to the mercury lamp. 

* De Groot's formula 2 is based upon data taken up to 150 atmospheres and 550 
volts per centimeter. It has been used here with values of gradient up to 750 
volts per centimeter, so that pressures above 150 atmospheres should be con- 
sidered as only approximately accurate. 


E. B. NOEL AND R. E. FARNHAM [j. s. M. p. E. 





FIG. 10. Variation in brightness across water-cooled 
mercury arcs operating at various pressures in tubes of 
2-mm. inside diameter. 



FIG. 11. Increase of temperature (Centi- 
grade) of a portion of the skin (lower arm) 
upon irradiation with light from tungsten 
lamps and water-cooled mercury arcs. For 
equal increases in temperature 4 1 / times as 
much mercury light can be employed as in- 
candescent lamp light. (E. G. Dorgelo, 
Technical Review, June, 1937.) 


Another way of illustrating the coolness of this light is by means of 
Fig. 11, which gives the relative increase of temperature of the skin 
with tungsten and with water-cooled mercury illumination. 4 For 
equal increases in temperature 4 x /2 times more mercury illumination 
can be used than tungsten. This is important for many applications. 

Operation of the Lamp. On 60-cycle a-c. operation there is a pro- 
nounced 120-cycle flicker, which is clearly evident in Fig. 12. By 
operating three lamps on three-phase the flicker can be sensibly 
eliminated as shown by the oscillogram of Fig. 13. 

FIG. 12. Current, voltage, and light traces for 1000- 
watt water-cooled mercury arc operating on a 60-cycle 

The lamps reach full brightness within a second or two after the 
switch is closed. Since their heat storage is small and cooling rapid, 
unlike the air-cooled high-intensity lamps they may be restarted at 
once after the current has been turned off. 

During life the lamp voltage gradually increases and the current 
and wattage decrease. The useful life is terminated by failure to 
start or by fracture of the quartz bulb. Although the operating pres- 
sure is high, the volume is so small that failures are not violent. How- 
ever, because the lamp is surrounded by water the outer jacket is 
subjected to a shock when a lamp fails and may crack, presenting a 
possible hazard of high voltage and running water. Where necessary 
a switch actuated by water line pressure can be installed to turn off 
the power should a jacket break. 

232 E. B. NOEL AND R. E. FARNHAM [j. S. M. P. E. 

The life of the lamp is dependent upon the number of times it is 
started and the type of service in which it is used. Although still 
in the developmental stage it is felt the life is satisfactory for many 
special applications. 

Equipment. For a-c. operation of the 1000- watt lamp the high- 
reactance transformer shown in Fig. 14 is used. The secondary sup- 
plies 1200 volts on open circuit for striking the arc. At the instant 
of starting, the arc voltage is so low that it is practically a short cir- 
cuit on the winding, and the impedance of the unit limits the current 



-- P ^^*fc,. 

FIG. 13. Oscillograph of ripple in combined 
light output of three lamps operating on a three- 
phase 60-cycle supply. 

in this case to 2.6 amperes. As soon as the inside tube walls become 
warm the pressure builds up and the voltage increases to 840 volts, 
while current automatically drops to 1.4 amperes. 

The lamps operate on ballasted direct current with about 15 per 
cent less current than on alternating current. D-c. operation is in 
many ways more satisfactory, but the generator or rectifier equip- 
ment is much more bulky than the transformer. 

The lamp may be run for 15 to 30 seconds in dish or bulb filled with 
glycerine, but for any longer periods of operation it must be run in 
flowing water. The lamp surface must be cleaned occasionally with 
dilute HC1 to remove deposits, the frequency depending upon the 
salts in the water supply. Recirculating cooling systems have been 


built employing a pump and radiator, but even then it is necessary 
occasionally to clean the lamp. 

Several kinds of sockets have been designed for this lamp, depend- 
ing upon the use intended. Fig. 15 shows a different type of single 
unit in which the replaceable part is merely the lamp itself with brass 
ends. Figs. 16 and 17 show two styles of jackets employing three of 
this same kind of lamp. 

Since the lamp is still in the developmental state, actual experience 
with its possible applications is limited Any analysis of the possible 
future application of the water-cooled unit must, accordingly, be 

FIG ; 14. Transformer for operating 1000- 
watt water-cooled mercury lamp on 110- or 
220-volt, 60-cycle lines. 

based upon a consideration of the characteristics of the lamp with 
respect to the requirements of the several potential services. 

The forms of lamp illustrated above provide maximum perform- 
ance, ease of replacement of the elements, and compactness. Some 
modification of present forms may be necessary for adaptation to a 
particular service; but the capillary tube is an essential feature and 
fixes the width of the lighting element. In summary, the chief char- 
acteristics are these : 

(1) Source dimensions. 1 mm. by 25 mm. for 1000 watts. Complete assembly 

(2) Light output. 65 lumens per watt ; steady on d-c. ; cyclic variation almost 
reaching zero on single-phase a-c. but causing only slight ripple on three-phase 



[J. S. M. p. E. 

(3) Power supply. High voltage (840 volts a-c., or d-c. for 1000 watts); 
current 1.4 amperes a-c., 1.2 amperes d-c. 

(4) Source brightness. 30,000 candles per square-centimeter. 

(5) Light distribution. Characteristic of a linear source of light. 

(6) Spectrum. Continuous, but with most of the light emanating from peaks 

FIG. 15. Socket and jacket combined, in which 
the replaceable element is the lamp itself, shown 
on the right. 

at 5600 A (yellow-green), 4350 A (blue-violet), 4100 A (violet), and 3650 A (near 

(7) Cooling system. Circulating water, self-contained system or from mains. 
More than 90 per cent of infrared (heat) radiation absorbed by circulating water. 

The following discussion will serve briefly to indicate the effect of 
such characteristics upon several phases of lighting for photography 
and projection. 


Black-and-White, and in Color. The high brightness and concen- 
tration of source provide the requisite beam control and efficiency of 
light utilization with both lens and reflector equipments. To pro- 



vide an adequate amount of light several capillary elements may be 
grouped together in a single reflector or equipment. The color of the 
light is satisfactory for black-and-white photography, although the 
"red" of the properties may have to be intensified for correct rendi- 
tion. A definite advantage in respect to the comfort of the actors 

FIG. 16. Socket for three lamps for single- or three-phase 
operation, with the lamps in a triangular arrangement. 

results from the very small proportion of infrared radiation. The 
spectral quality of the light is not adapted to present color processes, 
nor can it be rendered suitable by filtering alone. 

The camera shutter or the movement of the film must be syn- 
chronized if the lamps are operated on a single-phase a-c. supply. 
Direct current or the combination of several elements on three-phase 
alternating current eliminates this requirement. The cooling system 
should be self-contained, since portability of equipment is important 
in studio practice. 

236 E. B. NOEL AND R. E. FARNHAM [j. s. M. P. E. 

Ultra Speed. The extremely high light-intensities necessary for 
photography at 1000 or more pictures per second can easily be ob- 
tained because the compact equipment can be placed close to the area 
being photographed. But the greatest advantage is that there is no 
heat problem. For example, it has been possible to take 1000 pic- 

FIG. 17. Socket for three lamps, for single- or 
three-phase operation, with lamps arranged in 
a plane. 

tures per second, i. e., V^oooth second exposure on positive film at 
f/2.0 with no discomfort. 

Three-phase alternating or direct current are necessary unless 
single-phase alternating current of the picture frequency or a multiple 
thereof is obtainable. 

Trick and Background Photography, Animation, Tilting. For 
processes involving the illumination of a copy-board this linear source 
in a trough reflector of parabolic and cylindrical cross-section pro- 
duces high uniform illumination with minimum heat. Where a pic- 


ture is projected to a screen and rephotographed, the water-cooled 
lamp can be used as the projector light-source. Color photography 
is practicable to a limited extent by intensifying the reds. 

Film Printing. The relatively large proportion of ultraviolet 
radiation suggests the use of the water-cooled lamp for motion pic- 
ture printing and production of duplicate negatives. The high 
source brightness lends itself well to optical printers. Direct current 
is necessary where the film moves continuously. 

Sound Recording. Adaptability to optical control and the favor- 
able color of the light make it especially applicable to sound recording 
with both the light-valve and galvanometer systems. Direct current 
is necessary to eliminate parasitics. 


The color of the light from the liquid-cooled capillary lamp matches 
well the characteristics of the iconoscope, which is sensitive particu- 
larly to the blue-green. The suppression of the infrared is important 
in avoiding chromatic aberration. Since illumination levels must be 
very high, the cooler light is a boon to the artists. 


The length of the source is not too great to be efficiently utilized in 
a motion picture projector. The width is insufficient to fill the lens 
system unless a cylindrical surface is incorporated. Several sources 
and images may be aligned side by side to provide adequate illumina- 
tion for large screens. The color of the light seems satisfactory for 
black-and-white pictures. For color pictures, reds must be exagger- 
ated in the film. If the pictures are also taken under capillary lamps, 
the intensification of the reds would therefore have to be compounded. 


Two steps are involved in photoengraving: taking of the negative 
and printing on metal. For the former the copy-board must be il- 
luminated from the sides, a condition to which the line source of the 
water-cooled lamp lends itself admirably. Color copy is photo- 
graphed through red, green, and blue filters. Therefore, any dis- 
crepancy in the light output in the respective colors can be com- 
pensated for by the exposure ratios. The unmodified color of the 
mercury arc corresponds very closely with the requirements of the 
printing processes. 

238 E. B. NOEL AND R. E. FARNHAM [J. S. M. p. E. 


The same advantages that make the lamp applicable for printing 
on metal in photoengraving make it worth while for blue-printing, 
i. e., large amount of light of a color favorable to the sensitivity char- 
acteristics of the photochemical materials. 


There is no entirely satisfactory source now commercially available 
for enlargers used in making photo murals. The need for compact- 
ness, spectral quality favorable to the bromide emulsion, as well as 
freedom from heat, are amply met in the new source. 

Source shape, high brightness, and color will be found favoring 
conditions in other projection sources, such as searchlights and air- 
port lighting. In general, the water-cooling system can be either 
self-contained, with circulating pump or thermo-syphon, or connected 
to the city mains. Where portability of equipment is important 
self-contained cooling will obviously be indicated. 

In order to minimize high-voltage wiring, transformers may be 
incorporated in the equipment. For d-c. operation, a rectifier-filter 
system or a d-c. generator appear equally feasible. The transformer 
supplying the high voltage to the rectifier and filter can have high 
leakage reactance, thus practically eliminating ballast losses. The 
advantage lies with the generator when a number of lamps are to be 

In conclusion, it may be said that the ultra-high pressure quartz 
mercury lamp may find suitable application in several places in the 
motion picture field. Water-cooling and high voltage are necessary, 
and in some cases it may be desirable to employ a pressure-actuated 
switch to eliminate the hazard of running water and high voltage in 
the case of a jacket failure. The advantages are compactness, high 
efficiency, high actinic value, and remarkably high ratio of lumen out- 
put to radiated energy. 

The authors wish to express their thanks to D. D. Hinman, A. L. 
Shrider, M. A. Easley, and Dr. B. T. Barnes of the Lamp Develop- 
ment Laboratory at Nela Park for many of the measurements made 
on these lamps. 



1 "Eine Neue Lichtquelle Hoher Leistung," Das Licht (Apr. 15, 1935), No. 4, 
p. 84. 

BOL, C.: "Een Niewe Kwiklamp," Ingenieur, 50 (June, 1935), No. 24, p. 91. 

2 DEGROOT, W. : "Het Emissie en Absorptie Spectrum van Kivikdamp 
Bij Z. H. Drukken," Ingenieur, 50 (June, 1935), No. 24, p. 92. 

3 BARNES, B. T., AND FORSYTHE, W. E.: "Characteristics of Some New Mer- 
cury Arc Lamps," J. Opt. Soc. Amer., 27 (Feb., 1937), No. 2, p. 83. 

4 DORGELO, E. G.: "Water-Cooled Mercury Lamps," Philips Technical Re- 
view, 2 (June, 1937), No. 6, p. 165. 


MR. KELLOGG: Relative to the visible light, the ultraviolet of a high-pressure 
arc is very much less; but does it decrease as the wattage and pressure increase, 
or do they increase together, the visible portion increasing very much faster? 
Also, is the life with d-c. as long as with a-c? That is, for the same number of 

MR. NOEL: The life is good with either a-c. or d-c. The long-wave ultraviolet 
increases as the pressure is raised, but the short-wave ultraviolet in the neighbor- 
hood of 2537 A is absorbed. 

MR. RICHARDSON: I understand it is proposed to use several of these lamps to- 
gether, as a projector light-source. The light would have to pass through the 
water jacket and several thicknesses of glass. Would you be able to obtain the 
effect of a solid light -source? 

MR. NOEL: I believe so. The water absorbs infrared but not very much visible 
light; and since the water and glass are in contact there is little loss at that point. 

MR. KELLOGG : With regard to the light distribution, in spite of a large increase 
in the red as well as in the blue there is always a range of very little radiation, I 
should say, in the green. That is not due to absorption, is it? 

MR. NOEL: No, it is not. 

MR. DURAT: In using a bank of the lights, would it not be preferable to place 
them all in a single bath of water so as to have less refractive effect? 

MR. FARNHAM: I do not think we should try to control the light within the 
water unit. The water merely provides a means of getting the heat away from 
the lamp. 

MR. DURAT: I was thinking of an auxiliary water jacket, not to cool the lamps 
but to act as a medium through which the light could pass. 

MR. NOEL: I see no objection to that, although we have no trouble with the 
lamps we have shown. 



T. T. BAKER** 

Summary. Progress in two directions has greatly simplified making prints from 
screen-film negatives. The study of emulsion characteristics and of the mechanics 
of development with silver bromide solvents has led to the avoidance of color dilution 
in copying one screen material from another. Sodium thiosulfate in a metol de- 
veloper has been shown to localize development in the lower strata of the film, so that 
the silver image is formed in close contact with the reseau, largely eliminating scatter 
at the boundaries of differently colored units; the crystalline structure of the silver salts 
and grain-size frequency also assist in preventing scatter. Residual color dilution 
as the result of the 45 -degree oriented reseaux is explained, and the way in which this 
has been counteracted by suitable choice of gammas in the negative and positive ma- 
terial. The production of a vapor-lamp emitting the line spectra of mercury and 
cadmium without appreciable spectral background, combined with a liquid didymium 
chloride filter has provided a triple monochromatic light-source, the spectral lines of 
which coincide with the peaks of the reseau transmissions, thereby eliminating di- 
lution of color due to overlap, such as has always previously been present with color 
filters of the narrow-cut type. The Dufaycolor contact printing machine with auto- 
matic control of both hue and printing light is described. The technics of printing, 
and development with standard equipment, are described. 

A good deal has been said from time to time about the copying of 
one color-screen material upon another, the fidelity of the copies, 
and so on, and during the past two years a great deal more has been 
said about making screen positives from screen negatives. In this 
paper will be described the details of the negative-positive process, 
which has furnished a solution to making commercial screen-mosaic 
cine prints by the Dufay process. 

In talking about additive processes, it should be remembered that 
all color photographs are today taken by an additive analysis; that 
is, by recording the blue-violet, green and red components. But 
whereas in subtractive cases the separations are used as a basis for 
making continuous tone prints, in screen processes the negative 

* Presented at the Spring, 1938, Meeting at Washington, D. C. ; received 
May 9, 1938. 

** Dufaycolor, Inc., New York, N. Y. 




separations are usually reversed to positive, the one color matrix 
providing the additive filters for viewing by the retinal process of 

In Dufaycolor negative-positive technic the same matrix is used 
as base for both negative and positive emulsions. A photomicro- 
graph of it is seen upon the screen; the individual blue and green 
rectangles are approximately 19 to the millimeter. Taking one blue 
and one green rectangle, and the piece of red line contiguous as a 
complete "unit,'' the areas of the three elements 
are balanced so as to give white on projection. 
The average of a number of readings made on a 
special form of trichromatic colorimeter provides 
a numerical assay of the balance of the unit, and 
variations from neutrality are kept within limits 
of tolerance that have been agreed upon as the 
result of considerable visual test. This point is 
mentioned because, even with the precision con- 
trol of the relative areas in the unit, minute 
deviations invisible to the eye can suffice to cause 
off-balance in printing. The degree of off-balance 
in any particular reseau is measured, and a code 
number is obtained designating the minus-filter 
combination required to give the hue correction. 

The negative must thus be graded for color 
as well as density, and as printing is effected by 
light consisting of three monochromatic bands, 
the color correction is obtained by means of 
three sets of compensating filters each designed 
to reduce the intensity of one of the bands 
without affecting the others. Minus colors of the cyan, ma- 
genta, and yellow type, but actually complementaries of the reseau 
colors, are used, and these filters are dropped into the light- 
beam by means of light electromagnets operated by relays the ex- 
citation of which is controlled by metal staples in the perforations of 
a separate master film. The film is provided with two series of these 
metal staples, and passes through two distinct contact boxes; one 
contact box actuates the magnets introducing the necessary combi- 
nations of neutral gray filters to effect control of light intensity. 
The Lawley printer has lent itself well to these two methods of con- 
trol, the stapling being done on a full-length black-and-white print 

FIG. 1. CAD- 
vapor lamp. (Cour- 
tesy British Thomp- 
son-Houston Co., 
Ltd., Rugby, Eng- 

242 T. T. BAKER [j. s. M. P. E. 

from the negative so that the latter can not be mechanically dam- 
aged. A separate feed and take-up are provided for the control film. 

The light-source is of prime importance in making screen prints. 
Originally a Mazda lamp was employed, and narrow-cut gelatin 
filters, that removed from the white light those portions of the spec- 
trum that were common to any two of the reseau primaries. These 
overlap quite considerably, and the overlap is greatly magnified in 
printing, causing marked dilution of color. Such filters are very 
inefficient, and G. B. Harrison in England some time ago devised a 
light-source composed of a mixture of mercury vapor and red filtered 

Recently, however, cadmium has been introduced into high-pres- 
sure mercury- vapor lamps, and such a mercury-cadmium lamp, 
running at a pressure of about 1 atmosphere, has provided an elegant 
solution of the problem of producing a "tri-monochromatic" light - 

I . I . I . I . I . I . I . I . I . I . I . I . I . I . I 

FIG. 2. Mercury-cadmium lines. 

source. The cadmium-mercury-vapor lamp shown in Fig. 1 is at 
present made in England but a great deal of experimental work has 
been done on it in this country; much valuable information was 
published on the subject recently by Marden, Beese and Meister, 1 
who give the figures in Table I for the distribution of light from 
cadmium, as measured with a monochromator, thermopile, and 
galvanometer : 


Cadmium (% in Visible) 

Line Low Pressure High Pressure* 

6438 A 9.2 17.8 

5086 61.0 58.0 

4800 23.7 14.1 

4678 6.1 5.4 

* Corrected for eye sensitivity. 2 

Sept., 1938] 



The overall efficiency of the lamp is somewhat lower than that of 
the plain mercury type, the visible radiation being about 75 per cent 
only of the 10 or 12 lumens per watt mentioned by Dushman at the 
Fall Convention. 3 

, | . I . I .i . I . I . I . i . I. I. I . I . I . I . I 
40 * 

FIG. 3. Absorption of saturated solution of didymium 

The mercury-cadmium lines are shown in Fig. 2, and it will be seen 
that there is a very strong element of red, actually about 6 per cent, 
added to the familiar mercury line spectrum. Three lines are used 
for printing, one in the blue-violet, one in the green, and one in the 
red, at 643 m^u, 546 m/*, and 436 m/u- The remaining lines are ex- 


\---\-.\ '.I- 

- _ _ _- 





RI a lei 








FIG. 4. Showing relation of reseau to emulsion 

tinguished by means of a composite filter, the chief component of 
which is a 3-inch deep liquid cell containing a saturated solution of 
pure didymium chloride. The marked absorption of this salt is 
seen in Fig. 3. As luck will have it, the absorption bands come in the 
most fortunate places, totally eliminating, for example, the yellow 



[J. S. M. P. E. 

mercury lines, which would otherwise pass through both red and 
green reseau elements, causing green to add to red and so give orange, 
or red to add to green and so give orange-greens. The lamp can, of 
course, equally be used in an optical printer. 

When in 1928 the first serious attempts at negative-positive films 
were made in Paris, by Louis Dufay, Charles Bonamico, and the 
author we experienced considerable color dilution in making prints 
from the screen negatives. Several thousand feet of negative were 
made in the South of France, on 8-line per millimeter reseau, and 
prints from these on 15-line reseau were shown at the Pavilion 
Theater, London, nearly ten years ago! These pictures were scenes 
of an act by artists in an orange grove, and it is curious that the 





0<4 .08 .12 .16 .20 .M .28 32 


FIG. 5. Development in upper and 
lower layers of emulsion film. (Repro- 
duced from Phot. J.) 

oranges themselves and the blue-greens of the foliage were quite 
saturated, while all other colors were badly diluted. It soon became 
evident that two factors were at work in causing color dilution. Ir- 
radiation at the reseau element boundaries was one. The light 
scatter increased as the thickness of the insulating varnish layer be- 
tween emulsion and reseau increased; for this reason the thickness 
of the insulating coating was reduced to between 3 and 4 microns. 
The importance of this thickness from the point of view of scatter 
must be emphasized. The other cause was the decided overlap of 
the additive reseau colors. The reason for the purity of the orange 
and blue-green colors in these early prints was probably minimized 
scatter in these regions owing to very decided minima in the spectral 

Sept., 1938] 



sensitivity of our emulsion at that time. D. A. Spencer 4 in 1933 
drew attention to the results of light scatter within the emulsion 
actually the irradiation referred to and pointed out 5 that the de- 
saturating effect is common to negative-positive and successive re- 
versal processes. He also points out that the effect of a silver bro- 
mide solvent (ammonia, thiocyanate, thiosulfate, etc.), which is 
ordinarily used in first development in reversal processing, causing 
the degree of development occurring under adjacent color elements 
to become exaggerated, is offset by the opposite effect of scatter in 
subsequent reversal, but that it is not so offset when developing as a 


FIG. 6. Characteristic curve: upper curve: 
developed as negative in DK50; lower curve: 
reversed. (Note: The (lower) reversal curve 
has been plotted in reverse position for better 

negative. Spencer has found that by the use of hypo as a silver 
bromide solvent in the developer, the developed image is confined to 
the lower layers of emulsion grains that is, of course, those nearest 
the reseau, and is what we want (Fig. 4). The solubility of silver 
bromide is much greater in sodium thiosulfate solution than potas- 
sium thiocyanate or ammonia. One hundred grams of solution con- 
taining 10 grams of Na 2 S2O 3 at 20C will dissolve 3.50 grams of AgBr; 
a similar solution of potassium thiocyanate at 25 C will only dissolve 
0.73 gram of AgBr; 34 grams of NH 3 at 0C in 100 grams water dis- 
solve 1.987 grams of silver bomide. 6 A metol-caustic soda bath con- 
taining hypo (of the type given in a previous paper 7 ) is being used. 
Sodium thiosulfate added to a metol developer produces an increase 
in density, the increase rising to a maximum with increasing concen- 



[J. S. M. P. E. 

tration and thereafter falling off progressively, 8 but when the develop- 
ing solution contains a concentration greater than that that shows the 
maximum effect, it produces relatively more active development in 
the depths of the emulsion than in the surface layers (Fig. 5) . 

Scatter has to be prevented as far as possible by using emulsions 
of as fine grain as is consistent with the necessary speed; here the 
knowledge of the emulsion maker in preselecting symmetrically 
shaped AgBr crystals, adequately peptized, and an emulsion with a 
long grain-size frequency curve, has proved of considerable value. 
Increase in latitude is one of the most important features of the 
negative-positive process. Recent comparisons made of reversals 
against negatives developed in suitable baths show comparative 

latitudes (as measured on the 
characteristic curves between a 
7 of 0.25 at foot and shoulder), 
of 0.95 reversal against an 
average of 2.2 negative (Fig. 6). 
It is thus possible to deal in 
negative technic with a greatly 
improved range of lighting in- 
tensity. Control in develop- 
ment, however, is somewhat 
difficult, as with most emulsions 
applied in the low coating 
weight necessary for color- 
screen work,* gamma infinity is reached very rapidly (Fig. 7). We 
work, therefore, with very dilute baths. Dilution of color is inevit- 
ably caused in these prints where the negative and positive reseau 
elements cross, by microscopic white spaces occurring at the over- 
lapping corners; for this we endeavor to compensate by stepping 
up the gamma of the print to make the screen contrast as high as 
permissible, this having the physiological effect of increased satura- 
tion. The negative material has the red lines running at an angle of 
27 degrees to the edge of the stock, with the lines of alternate blue- 
green elements running at right angles. In print stock the lines are 
inclined at an angle of 45 degrees. This orientation is chosen so 
that there is no danger of moire when one reseau is printed on the 
other. But in printing it necessarily happens that there are portions 


f * 








1 2 

> 4 S * 

FIG. 7. Gamma-time curve. 

* About 60 mg. of silver halide per sq. decimeter. 


of many reseau elements that are overlapped by portions of ele- 
ments of another color, and in these local spots of double filtration 
not enough light is transmitted to produce a developable effect upon 
the emulsion; hence the spots appear white in the silver image, 
thereby causing the effect of color dilution. 

In split-beam camera work it is recognized that the separation 
must be substantially correct, and the balance of the three images 
correct, if satisfactory subtractive prints are to be obtained. It is 
equally important that in a screen negative the three intermingled 
images for after all there are three images be correctly balanced 
and in equally sharp focus. The latter is, of course, taken care of 
by choice of a reasonably apochromatic lens. But the color-balance 
needs to be quite accurate, compensation being possible in printing for 
lack of hue balance in the reseau rather than for mistakes in lighting. 
We are using Mole-Richardson arcs, the broadsides and scoops being 
used without the straw-filter; no filter is used on the camera. Pro- 
vided, as stated, the negative is correct, printing offers no problems 
other than the double grading for density and reseau hue.. 


1 MARDEN, J. W., BEESE, N. C., AND MEISTER, G. : "Cadmium and Zinc Vapor 
Lamps," Thirtieth Annual Convention of the Illuminating Eng. Soc., Buffalo, 
N. Y., Aug. 31 to Sept. 3, 1936. 

2 HOFFMAN, R. M., AND DANIELS, F.: "Photochemical Technique III, 
Quartz Capillary Arc Lamps of Bismuth, Cadmium, Lead, Mercury, Thallium 
and Zinc," /. Amer. Chem. Soc., 54 (Nov., 1932), p. 4226. 

8 DUSHMAN, S.: "Recent Developments in Gaseous Discharge Lamps," 
/. Soc. Mot. Pict. Eng., XXX (Jan., 1938), No. 1, p. 58. 

SPENCER, D. A.: Phot. J. (Jan., 1933), No. 1, p. 19. 

Idem: (April, 1937), No. 4, p. 251. 

SEIDELL, A. : "Solubilities of Inorganic and Organic Compounds," p. 602. 

7 BAKER, T. T.: "Some Lighting Problems in Color Cinematography," /. 
Soc. Mot. Pict. Eng., XXIX (Nov., 1937), No. 5, p. 471. 

8 MURRAY, H. D., AND SPENCER, D. A.: "The Addition of Silver Ion Reac- 
tants to Organic Developing Solutions," Phot. J. (July, 1937), No. 7, p. 458. 





Summary. The advisability of using a non-linear volume characteristic in dialog 
recording is discussed. In this connection consideration is given to the following 
points: (a) the difference of level existing between the original and reproduced 
speech; (b) the advantages of a system in which manual monitoring can be confined 
to overall level correction rather than to momentary peaks; (c) the advantage of limit- 
ing the range of all except trained voices to assure the highest possible intelligibility. 
An analysis is then made of the various types of compression possible and a terminol- 
ogy is developed. 

Consideration is given to the type of device most applicable to motion picture record- 
ing. The electrical circuits and operating characteristics of a compressor that has 
been in commercial service for 18 months are discussed. Practical results and ad- 
vantages obtained by the use of the device during this period are analyzed and the 
possibility of addition applications is indicated. 

At RKO Studios, in 1936, we began investigating a type of annoy- 
ing volume expansion present in our variable-area dialog recording 
which, for brevity, we named the "jumps," the difficulty consisting 
of very sharp volume increases in speech, some cases affecting a single 
word and at other times a syllable within a word. Upon comparing 
our product with variable-density recording, we felt that the effect 
was absent from the latter. At that time there was insufficient vari- 
able-area recording available from other studios to permit arriving 
at a general conclusion ; however, we felt that the effect was present 
in all variable-area recording. Our first observations led us to 
believe that variable-area recording suffered from inherent volume 
expansion but extensive tests failed to reveal it. 

In the course of our investigation, we found that the average level 
used by variable-density licensees was such that the high-amplitude 
peaks, which apparently caused the trouble, were being recorded 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 11, 1938. 

** RKO Radio Studios, Inc., Los Angeles, Calif. 



over the non-linear portion of the H&D curve, and were being ef- 
fectively compressed. In addition, instantaneous peaks of shorter 
duration than the operating time of the anti-ground-noise bias were 
receiving further compression. Numerous theater listening tests 
proved that this type of recording had superior volumetric smooth- 

The desirability of recording dialog with a non-linear volume char- 
acteristic becomes apparent on examination of recording and repro- 
ducing conditions. 

The average level of theater speech reproduction is 15 or 20 db. 
greater than the original speaking level. In arriving at a proper over- 
all frequency response, this fact is taken into careful consideration, 
but until now, has not been regarded as important in relation to 
volume range. At normal speech loudness, that is, at the level at 
which speech is heard without artificial aid, considerable volume 
latitude is permissible without annoyance. When this average speech 
is reproduced some 20 db. higher without compression of momentary 
peaks, the loudness at these points causes the listener extreme an- 
noyance. This condition is true when the average reproduced level 
is no greater than is necessary for good intelligibility. Poor repro- 
ducer frequency characteristics or high theater reverberation serve 
to heighten the effect. The energy peaks are not necessarily ex- 
pressive dynamics used by the actor, but may be caused by lack of 
breath control or other vocal defects, and the less trained the actor 
the more noticeable the difficulty. However, the dynamics of even 
the well trained voice are uncomfortably exaggerated when repro- 
duced at theater loudness. These observations lead to the con- 
clusion that compression of variable-area recording would be de- 

In the operation of recording equipment, additional advantages 
accrue from the use of a non-linear volume characteristic. The dif- 
ficulty of producing a smoothly monitored scene containing good 
dramatic quality and at the same time confining it within the range 
necessary to record it on the sound-track is evident. The fact that 
a compressor will take care of a wide input range makes constant 
twisting of the gain control unnecessary, and results in a superior 
product free from improper levels of short duration which can never 
be corrected. 

In considering the characteristics of a device to be used for solving 
these problems, two distinct types were available: 

250 J. O. AALBERG AND J. G. STEWART [j. s. M. P. E. 

(7) The "limiter." 

(2) The "compressor" or non-linear amplifier. 

The two devices are electrically similar, differing only in opera- 
tional adjustments. In fact, a single amplifier, by proper adjust- 
ment, will perform either function. There is, however, considerable 
difference in the results obtained with the two types. 

To avoid confusion in terminology, the following terms are used in 
discussing compression characteristics. Two levels must be desig- 
nated in order to fix the operating limits of such a device : 

(1) The input level at which compression starts, i. e., the device being linear 
below this point. 

(2) The input level at which the compressed output reaches full track or 100 
per cent modulation. 

Considering the compressed range as starting at the first point and 
ending at the second, we may speak of compressing so much input 
within these limits. For example, if compression starts at 10, 
considering full track to be zero level, and the input must be raised 
25 db. before reaching zero level output, then the device compresses 
25 db. into 10 db. 

The limiter type is designed, as its name indicates, to compress a 
large input range into a small output range. In the terms outlined 
above, such a device compresses 10 or 20 db. into 2 or 3 db. When 
recording with such a device, if the gain is set at a point to permit a 
reasonable amount of dynamics, the limiter will be actuated only by 
extremely high input level peaks, and will not assist in smoothing 
out the average dialog levels. If, on the other hand, the gain is 
raised to a point where the limiter is being actuated by average 
dialog levels, the resulting product will have very limited range and 
will be devoid of desirable dramatics. With the compressor type, 
non-linearity starts below the point of average dialog level, for ex- 
ample, 10 db. below full track, and compresses 20 or 25 db. into 10 

Recordings were made on both types, and the compressor was 
found superior for motion picture work, one advantage being that 
the degree of compression remains constant over a large range of 
input. In other words,- the input vs. output characteristic of the 
device consists of a linear portion up to the 10 point, and above 
that, a straight line of slope less than unity, the slope of the second 
portion being determined by the amount of compression. This 


allows great operating leeway and produces a product of sufficient 
range but free from disturbing volume peaks. For these reasons, 
it was preferred and finally adopted at RKO Studios, where it has 
been in use for eighteen months. 

Non-linear amplifier design has been well covered in technical 
papers and magazine articles. The amplifier in use, however, has 
the advantage of being adjustable over a wide range of character- 
istics covering both limiter and non-linear types. Two adjustment 
controls are used. The first adjusts the fixed bias on the rectifier, 
which is always biased to or beyond cut-off. This determines the 
point at which compression starts. With no bias, the amplifier is 
non-linear over its entire range. As the bias is increased, the start- 
ing point is moved progressively to higher levels. The second con- 
trol adjusts the input signal voltage supplied to the rectifier which 
determines the slope of the curve above the starting point, i. e., the 
total amount of compression. 

For present conditions of recording, a starting point between 6 
and 12 db. below full track, depending upon the recording level in 
use, has been chosen. This introduces sufficient compression with- 
out dangerously reducing the ratio of normal dialog to set noise and 
reverberation. In setting the second adjustable factor, the total 
compression, a compromise must be reached between ease of opera- 
tion and good dynamics in the product. A range of 12 db. in speech 
seems sufficient for good dynamics, and a setting based upon this 
range results in satisfactory operating conditions. For our present 
recording level, this is accomplished by a starting point 10 db. down 
from full track and the compression of 20 db. into this 10. 

The operating time constants of the device are adjustable. Under 
ideal conditions compression would take place instantaneously, and 
a sufficient return delay would be used to prevent the device from 
operating during a full cycle of the lowest recorded frequency. In 
practice, the compressor is used with an 80-cycle high-pass filter, 
and the return to normal timing is adjusted to between 25 and 50 
milliseconds. If the return is made too rapid, the device oscillates, 
and if too slow, low-level periods appear immediately after high-level 

When recording with a non-linear volume characteristic, several 
problems are encountered. Large loudness differences may exist in 
a compressed signal with small variations in peak amplitude. In the 
extreme case of the limiter type, scenes having the same peak indica- 

252 J. O. AALBERG AND J. G. STEWART fj. s. M. P. E. 

tion may vary to the ear as much as 6 db. in loudness. For that 
reason, reliance must be placed upon aural monitoring, since com- 
mercial high-speed visual indicator meters tend to read peak values. 

It has been our experience that the compression characteristic of 
the device tends to reduce the effect of frequency attenuation placed 
before it. With increasing input level, the frequency output of the 
channel tends to become flat. It is possible that some advantage 
may be obtained by splitting the attenuation, placing part before 
and part after the compressor, to arrive at some balance that will 
result in a desirable change of frequency characteristic as the level 
increases. The effect is noticed also as a tendency to compensate 
for momentary acoustical or electrical peaks regardless of their 
source and to reduce somewhat variations in quality due to micro- 
phone peaks and room reflections. 

The device provides additional ground-noise reduction by making 
it possible to record at higher average modulation without danger 
of overshooting. Improvement in this direction is attained even 
though the product may later be re-recorded at a lower level to ob- 
tain "Hi-Range" effects. 

There are re-recording requirements to which the limiter is better 
adapted than the compressor type. In scenes where dialog is re- 
recorded with very high background effects, intelligibility is greatly 
improved by the use of excessive compression of the dialog. This 
is best accomplished by the use of the limiter. 

Careful observation of our compressed product under a wide vari- 
ety of theater conditions has shown the absence of the effect that was 
erroneously regarded as volume expansion, thus making it possible 
to reproduce the product at higher average levels with a consequent 
improvement in intelligibility. The occasional error of using ex- 
cessive dialog compression was evidenced by a lack of proper dy- 
namics in highly dramatic sequences, with resulting loss of screen 

While the RKO Studio experience has been confined to the use of 
this device in variable-area recording, all that has been said seems 
to apply equally to linear variable-density recording. 


MR. FRAYNE: I question some of Mr. Aalberg's theses. In regard to the 
statement that the blasting effect that is present in variable-area recording is 
absent in variable-density due to the flattening off of the characteristic curve, it 


is possible to process variable-density recordings with practically no flattening off 
of the high modulation if the proper print density is chosen. As you know, it is 
customary in turning out release prints to vary the density over a very wide 
range. In doing that I have not observed any evidence that as we go from the 
flattened out area into the linear area we get this effect. In one Hollywood studio 
at the present time the compression in speech with the processing they use is of 
the order of only about 1 db., yet there is no evidence whatever of this blasting. 

I have also heard recently some variable-area recordings made with a device 
other than a galvanometer in which the blasting was not present, so I feel that 
Mr. Aalberg must be correcting for some fundamental deficiency in the recording 

MR. KELLOGG: Mr. Frayne states his belief that compression in variable-area 
recording is needed because of some inherent defect in the equipment that results 
in an opposite effect or "volume expansion." Messrs. Aalberg and Stewart state 
in the paper that at first they had the same idea, but on further study gave up the 
theory. The galvanometer is usually the first device suspected. It has been 
subjected to the most rigorous tests. Saturation if present in appreciable magni- 
tude, would give some compression, rather than the volume expansion which would 
have to be compensated by a compressor. Owing to the large ratio of air-gap to 
iron reluctance, hysteresis produces a negligibly small wave distortion. Hys- 
teresis loss is relatively greater at low levels, as is well known. Measurements on 
our older galvanometers indicate that it could account for no more than 2 db. loss 
when the level is 40 db. below full modulation, an amount entirely too small to 
account for the criticism, and in our newer design this loss has been reduced to 0.5 
db. Film-transfer loss has been equally carefully studied, and again we find 
linearity down to the lowest signals that it is practicable to measure. It was con- 
siderations such as these that led the authors of the paper to abandon the theory 
that there was volume expansion inherent in the system or equipment. Of 
course almost anything is possible with bad adjustments or processing. For ex- 
ample, with too narrow a zero line and badly fogged prints we can produce volume 
expansion, but such conditions are the result of outright carelessness, and are 
clearly not what the authors are talking about. 

We come then to the question of whether the speech as it reaches the micro- 
phone can often be ' 'jumpy. ' ' Of course, it can. We all know hundreds of people 
who talk that way, and at a little distance, or with some room echoes, they are ex- 
tremely difficult to understand. When the level is raised above normal, as in 
theater reproduction, the jumpy effects, as the authors point out, are more notice- 
able and more annoying. 

Turning now to the question of whether the variable-density track affords com- 
pression, it is, of course, admitted that so long as the conditions for straight-line 
or classical variable-density are adhered to, compression does not take place, and 
the observations that Mr. Frayne mentions are for these conditions. It is my 
understanding of the paper that the authors believe these conditions to be ex- 
ceeded in practice so much of the time that a very substantial amount of com- 
pression is experienced. 

MR. ALBERSHEIM: In experimenting with the variable-area recording method 
we found, as pointed out by Mr. Kellogg, that variable-area sound-tracks over- 
load more suddenly than variable-density records. It may be that the blasting 

254 J. O. AALBERG AND J. G. STEWART [j. s. M. p. E. 

occurs only when overload takes place, and is due to the type of harmonics pro- 
duced by cutting over the edge of a sharply limited sound-track. I have heard 
some variable-area recordings made at our East Coast laboratories that produced 
this same sharpness of blasting; at the time I believed it to be due to the genera- 
tion of disagreeable high harmonics such as are sometimes produced in class B 
amplifiers. Therefore, if one avoids overload or sees to it that the overload dis- 
tortion takes place gradually, that is, without sharp discontinuities, the blasting 
will be reduced. 

MR. KELLOGG: I would not deny for a moment that overloading, which, of 
course, frequently occurs in both kinds of records, may accentuate the impression 
of blasting and jumpy effects. But from what Mr. Stewart and Mr. Aalberg have 
to say about it, this jumpy quality is not confined to cases where there has been 

MR. FRAYNE: I have seen some oscillograph records of variable-area dialog 
recently in which a certain amount of this blasting effect had been noticed; and 
it was quite noticeable that even where the modulation was within 15 db. of the 
top the blasting was still present. So I do not believe that the overload is entirely 
responsible for the quality. It is true, of course, that variable-density overload 
is more gradual than that found in variable-area recording. 

MR. KELLOGG: We have made laboratory tests that entirely checked the ob- 
servations that Mr. Albersheim mentions, namely, that the gradual overload- 
ing of variable-density is more tolerable to the ear than overload in a variable- 
width system. This, plus the fact that it is almost impossible to judge an over- 
loaded density track by eye, would almost inevitably lead to the result that a great 
deal of overloading is permitted in density tracks. The fact that a true straight- 
line density track would be as much as 5 db. below a variable-area track in out- 
put, but that theaters do not have to make nearly that much adjustment to main- 
tain about equal average loudness, is further evidence of the wide prevalence of 
overloading. This is not a criticism of the practice of the sound departments 
using variable-density. Compression has been found definitely to be useful, and 
they would be foolish not to take advantage of the characteristics of the system 
up to the point where the benefits from compression are more than offset by the 
harmful effects of distortion. What Messrs. Aalberg and Stewart say (and we 
say it, too) is that it is still better to use electronic compression and a track that 
is not overloaded. To take care of occasional overloads, a more gradual overload- 
ing characteristic can be had in the variable-width system by suitably shaping 
the mask in the recording system. 

The authors mention the fact, based upon their tests and observations, that 
when speech is reproduced at an unnaturally high level, some compression is de- 
sirable, which might not be called for if the reproduction were at natural level. 
Although I do not know whether this relation has been pointed out before, it seems 
entirely reasonable. 

The reasons are probably of two kinds: First, irregular, loud sounds can be ir- 
ritating and tiresome, although the same sounds, with the same total db. volume 
range, could be reproduced at lower level without any such irritating effect. In 
the second place, some compression would undoubtedly be justified in view of the 
non-linear effects of masking. If loud syllables are quickly followed by weak 
ones, any reverberation results in difficulty in hearing the weak sounds, and obvi- 


ously if, by means of compression, the difference in loudness can be reduced, articu- 
lation will be improved. This much is true, regardless of the level of reproduction. 
The non-linear masking factor, however, results in making matters worse as the 
level is raised. The loud, voiced vowels which produce the troublesome rever- 
beration are, for the most part, in the range below 1000 cycles, while the mounds 
that are likely to be lowest are, for the most part, of much higher frequency. 

In Speech and Hearing (p. 169) Fletcher shows the results of a large number of 
masking tests. In each group of curves, the frequency of the masking tone is 
shown above and the frequency of the tone that is masked or drowned out is given 
on the scale at the bottom of the figure. Taking, for example, a masking tone of 
400 cycles, the curves show that the threshold intensity for a 2000-cycle tone 
is not appreciably affected until the 400-cycle tone has reached 40 db. above its 
threshold. If the level of the 400-cycle tone is raised from 40 to 60 db., the level 
of the 2000-cycle tone must be raised 18 db. in order to be audible. Raising the 
level of the 400-cycle tone 20 db. more, or from 60 to 80, makes it necessary to 
raise that of the 2000-cycle tone 32 db. to make it again audible; and if the 400- 
cycle tone is again raised from 80 to 100, the 2000-cycle tone must be raised 28 
db. more. Similar effects are shown for masking-tones of 200 and 800 cycles. 
In view of the measurements just quoted, we should certainly expect that the 
masking effects of the "hangover" of a loud low-frequency sound would become 
worse as the levels are raised. This is not saying that the overall articulation will, 
in general, be impaired by raising the level, for there is an opposing factor, espe- 
cially where room noise is present and some sounds may be even below threshold. 
Under such conditions, raising the entire level, of course, improves articulation 
and it would not be until quite high levels are reached that the loss due to abnor- 
mal masking would offset the gain resulting from raising the levels of the fainter 
sounds. Compression, of course, helps articulation by raising the level of the 
faint sounds and also by reducing the masking if some reverberation is present. 

MR. FRAYNE: Mr. Kellogg's remarks are extremely interesting, but they do 
not explain to my satisfaction why the effect is found only in variable-area rec- 
ords and not in variable-density records, where, up to the overload point, no 
considerable degree of compression is noticeable. 

MR. AALBERG:* Mr. Frayne's observations are evidently based upon material 
other than standard studio recordings. Obviously there exists a misunderstand- 
ing among the users of variable-density recording systems as to the true magni- 
tude of momentary peaks present in speech recording. Due to the very definite 
overload point on the variable-area systems, users of this type of track have 
always been concerned about peak values. We have compared the peak input 
levels of histrionic speech with simultaneously recorded variable-area and vari- 
able-density track output peak levels and found surprising compression in the 
density system. 

* Communicated. 



Summary. The transmission of television signals over wire lines a number of 
years ago used signals corresponding to images of coarse detail, and required frequency 
bands accommodated by existing types of circuits. The television images now con- 
sidered necessary correspond to frequency bands of greatly increased width, and re- 
quire special wire networks and transmission means. 

The coaxial conductor recently in operation for experimental purposes between New 
York and Philadelphia can transmit a band of frequencies of approximately 1000 kc. 
While designed primarily for multiple telephone channels, it offered the possibility 
of transmitting a single wide band as required for television. 

The experiment consisted in providing television-type terminal apparatus for pro- 
ducing signals falling within the available band, and of developing and utilizing 
methods of transmission that would make most complete use of the frequency band 
available. For convenience in experimental work, the signals were generated from 
motion picture film. The film was scanned mechanically by means of a lens disk 
containing 240 lenses. The film was moved continuously 24 frames per second, and 
iL motion, together with the motion of the lenses in the disk, swept each frame of the 
film in 240 juxtaposed lines. Light passing through the film was received on a photo- 
sensitive surface; the resulting photoelectric current was amplified and by means of 
modulating and demodulating apparatus transmitted as a single side-band between 
approximately 150 and 950 kc. At the receiving end the single side-band signal was 
restored as a signal from zero to 800 kc. 

For reception, special cathode-ray tubes were used in which particular attention 
was paid to the definition of the spot and the linearity of response. Synchronism be- 
tween the two ends was obtained by sending a single ft equency over a separate channel 
and using it to operate sweep circuits at the receiving end. The use of mechanical 
scanning and the high-definition receiving tubes resulted in pictures of very satisfactory 
quality within the limitations set by the frequency band. 

The experimental transmission of motion pictures over the coaxial 
cable between New York and Philadelphia, which was demonstrated 
in November, 1937, was not primarily an experiment with motion 
pictures. Motion picture film was used in the experiment as the most 
convenient means for producing a controllable picture signal, capable 

* Presented at the Spring, 1938, Meeting at Washington, D. C. ; received 
April 20, 1938. 

** Bell Telephone Laboratories, New York, N..Y. 


of indefinite repetition under identical conditions for test purposes. 
The test was not planned or carried through with direct reference to 
the special problems that may be presented by motion pictures as 
television material, and it is therefore to be expected that many 
questions that will occur to motion picture engineers will not find 
their answers in this account of the experiment. Furthermore, it 
should be made clear that the experiment was, from the standpoint 
of the communication engineer, one of several whose general purpose 
was to test the capabilities of the coaxial transmission line for carry- 
ing a wide-band signal. In previous tests the possibilities were in- 
vestigated of providing a very large number of separate telephone 
channels (some 240 for these tests) each requiring relatively narrow 
frequency bands. In this test, the problem for study was the possi- 
bility of faithfully transmitting signals requiring a single very broad 
band of frequencies, that is, signals of the television type. 

The instrumentalities of the project fall naturally into two groups. 
One group comprises the terminal apparatus, whose function is the 
generation of electrical signals from the light coming from the "scene" 
to be transmitted, and the transformation of the electrical signals, 
after transmission, back into a satisfactory counterpart of the origi- 
nal scene. The other group comprises the transmission means, and 
the associated apparatus that puts the signals from the sending end 
apparatus into form for most efficient transmission, and recovers 
the signals after transmission in suitable form for use by the receiving 
end terminal apparatus. 

While the two groups of apparatus are different in character, the 
first being largely optical, the second largely electrical, there is a 
very close interrelation of requirements and limitations which de- 
manded at the start certain decisions on the character of the picture 
that it was planned to transmit. These decisions are listed below, 
with some of the reasons leading to them : 

A dominating consideration in this work was to make the most 
efficient use possible of the frequency band width available in the 
coaxial cable and associated apparatus. This is essentially an eco- 
nomic consideration, for band width has a definite money cost. The 
starting point in planning the system is then the frequency band 
available. Without going into the considerations that determined 
the characteristics of this particular coaxial cable, it suffices here to 
state that the upper limit of frequency satisfactorily handled by the 
cable and its associated repeaters was about 1000 kc. This does not 



[J. S. M. P. E, 

mean, however, that television signals occupying a band from to 
1000 kc. can be accepted for transmission. The first difficulty en- 
countered is that immunity from external disturbance, which is 
characteristic of the coaxial structure, does not extend to the lowest 
frequencies. These are, however, an essential part of the television 
signal. Recourse must therefore be made to the use of a "carrier" 
frequency which lifts the whole frequency band to be transmitted to 
a higher value. When this is done, by the methods commonly used 




TOP FREQUENCY = 240 X 240 X X X 24 =606.4 KILOCYCLES 

FIG. 1. Relation between picture elements, frame repeti- 
tion frequency, and band width for transmission. 

in radio the signal is transmitted as two "side-bands," one to each 
side of the carrier, each occupying the entire frequency band space 
of the original signal. If this double-side-band method were used 
with our coaxial cable it would mean that our signal band would have 
to be less than half of the 1000 kc. or 500 kc. in width. 

This factor of x /2 would mean a very serious loss, to be avoided if 
possible. A method of avoiding this loss, at the same time utilizing 
the carrier method of placing signals at a desired place in the fre- 
quency band is offered by "single-side-band transmission." This 
method, as utilized in this experiment, places the single side-band 


between approximately 120 and 950 kc., thus furnishing a useful 
frequency band of over 800 kc. 

Taking this frequency band as a starting point we can determine, 
by calculations that are now conventional in connection with image 
transmission, the number of scanning lines to use in our image 
analysis. One variable in this calculation is the number of image repe- 
titions per second. With our choice of motion picture film as our 
source of images, this repetition frequency is most conveniently taken 
as the standard frame frequency of 24 per second. Another variable 
is the shape of the picture, or frame. This was chosen close to the 
4:3 ratio of dimensions common in film; actually, because of space 
clearances needed in the apparatus, with scanning in the long direc- 
tion of the rectangle, the ratio finally used was 7:6. Using these 
figures we arrive at the number of scanning lines to utilize the avail- 
able frequency band as follows: the number of picture elements, 
assumed square, to fill the 7 : 6 area will be the product of n (the 
number of scanning lines) by 7 /&n, by / (the repetition frequency). 
Now, a single signal cycle consists of an alternation of light and dark, 
which may be considered as two picture elements, as illustrated in 
Fig. 1 . We therefore have, if we call the top frequency F, 

F = Va X n X 7 /&n X 24 

Taking F as 800 kc., this gives us for n very approximately 240. On 
the basis of these considerations, therefore, a choice of 240 scanning 
lines was indicated as the upper limit capable of use with the trans- 
mission line. 

In the early stages of the work, and paralleling the coaxial cable 
development, a study of the relation between picture quality and the 
size of picture elements was made using motion picture films printed 
out of focus. By correlating the known size of the circle of confusion 
in these films with the size of the elements in a television image, with 
reasonable allowances for the effects of the differences in image struc- 
ture, it appeared that a 240-line image should be capable of giving a 
picture not seriously inferior in quality to the average small home 
motion picture projector, provided comparable freedom from visible 
image structure were obtainable, with comparable contrast and 
fidelity of tone rendering. 

The use of 240-line scanning, with 24 frames per second, as de- 
cided upon for this experiment, deviates considerably from the figures 
of 441 lines, and 60 (interlaced) frames per second, which are now 



[J. S. M. P. E. 

being contemplated as "standard" for television. It was, however, 
believed that the principal questions presented by the problem of 
transmitting television signals could be satisfactorily answered by 
this study, and that the wider frequency bands demanded by the 
newer television standards can be handled by more or less straight- 
forward extensions of the means here used. 


FIG. 2. 

Diagrammatic representation of opti- 
cal system. 

Signal Generating Apparatus. The scanning apparatus chosen for 
this test was of the simplest type, namely, a scanning disk. The 
disk was made from a saw blank 6 feet, in diameter; near the pe- 
riphery of which were mounted, at identical radial distances, 240 
lenses, each consisting of a pair of plano-convex elements. The 
focal length of the compound lenses was approximately 1 inch, and 
the diameter ultimately used was about 3 / 8 of an inch. 

A schematic diagram of the optical system used is given in Fig. 2, 
while Fig. 3 shows a photograph of the disk housing with the film- 
driving mechanism at the top. The light-source was a ribbon- 
filament tungsten lamp, operated on direct current, which was 

Sept., 1938] 



imaged by means of a condensing lens upon a square aperture. This 
aperture was at the focus of a collimating lens past which the lenses 
in the disk moved. Each disk lens formed a sharp image of the 
aperture and, as the disk rotated, this image was moved across the 
film at the focus of the lens. The film was moving continuously so 
that successive lens images scanned successive lines on the film. In 

FIG. 3. 

Scanning disk used for generating signals from 
motion picture film. 

order to carry the light after transmission through the film to the 
photosensitive surface, a light- tunnel was used consisting of a rec- 
tangular bar of highly transparent material (Pontalite) in which, 
through multiple total reflection, the light was caused to emerge at 
the far end with uniform intensity from all positions of the scanning 

On emerging from the light-tunnel the light falls upon a photo- 
electrically sensitive surface, which is the first element of a 10-stage 
electron multiplier. The signal delivered by this device had a peak 



tf. S. M. P. E. 

value of 100 microamperes and is strictly proportional to light- 

For purposes of local test, before connecting this terminal appara- 
tus to the coaxial transmission system, a wide-band amplifier was 

FIG. 4. Cathode-ray tube used for reception of 
television images. 

used, with a range from 5 cycles per second to 1,000,000 cycles. In 
conjunction with this, in order to supply an equivalent for the direct 
current not transmitted, a "zero wander" current was introduced, 
which automatically brings the black at the end of each scanning 
line to a constant value. 


Besides the picture signal, the sending end apparatus must supply 
signals for synchronizing the sending and receiving ends. These 
were generated optically, using the same lenses as for the picture 
signals. Light flashes were produced from an auxiliary light-source, 
whose image was swept over a small slit. The brief light flashes 
(about 3 microseconds in duration) fall upon a second electron multi- 
plier, the output of which is amplified to give pulses which trip a gas- 
filled tube and yield a saw-tooth wave. This saw-tooth wave is 
used in the local testing to control the sweep circuits of the cathode- 
ray receiving tube. For transmission purposes the saw-tooth wave 
is filtered to produce a 5760-cycle sine wave. This frequency is 
transmitted by the carrier equipment to the distant end, and there 
pulses are produced to control sweep circuits in the receiving ap- 
paratus. The sine wave produced by the light flashes was used also 





FIG. 5. Construction of cathode-ray tube. 

to beat with the output of a 5760-cycle precision tuning fork, to ac- 
tuate a speed-control circuit by means of which the speed of the d-c. 
motor used to drive the disk could be held constant to one part in 

Receiving-End Apparatus. The receiving device chosen was the 
cathode-ray tube, and a special precision type was designed for this 
test by Dr. C. J. Davisson, attention being directed to the construc- 
tion of a tube that should give the highest possible fidelity of detail 
and tone rendering, quite irrespective of cost and of considerations 
that might enter were commercial production contemplated. 

The special features of the tube that contributed to its excellence 
as a testing tool are best brought out by a description of its essential 
elements. Fig. 4 is a photograph of the tube and Fig. 5 is a schematic 
diagram of its construction. It was made of very considerable length 
(5 feet) in comparison to the size of the field (7X8 inch) , in order to 
minimize distortion. The deflection of the beam was controlled in 



[J. S. M. p. E. 

both directions electrostatically. In order to provide a sharply de- 
nned rectangular spot whose dimensions across the scanning line 
should not change, an electron lens system is provided that forms a 
narrow beam of electrons from a hot filament onto an aperture 
0.006 inch square. Between the lenses and the aperture are two 
modulating plates (actually two cross-connected plates to insure 
parallel displacement of the beam without any angular component) 

8 10 12 14 16 

FIG. 6. Characteristic of special cathode-ray tube. 

connected to the incoming circuit in such a way that the potentials 
of the plates vary according to the strength of the incoming signals. 
The electron beam is thus deflected so that more or less of it passes 
through the aperture and thence to the fluorescent screen on the 
front of the tube. The spot of light on the screen is consequently a 
rectangle, of constant height corresponding to the separation of the 
scanning lines, but of variable width in the direction that the spot is 
to be moved in scanning. When swept across the screen these spots 
of constant height produce lines of light, which, with accurate sweep 


control to juxtapose the lines, result in a very uniform structureless 
field. The light from the variable-sized spot should vary linearly 
with the strength of the signal for faithful reproduction of tone 
values. In Fig. 6 is shown the characteristic actually obtained on a 
representative tube. This shows the variation of beam current 
through the final aperture, to which the light from the fluorescent 
screen is closely proportional, as a function of the modulating voltage. 
The mechanical line-up of the electron lens elements is in this case 
such that the voltage corresponding to the accurate centering of the 
spot on the aperture is not zero as in the description above but about 
14, which is taken care of by a biasing potential on the tube. De- 
pending upon the polarity of the signals, either slope of the char- 
acteristic can be used; often one side will be definitely better than 
the other. 

In order to produce a picture the 'spot on the fluorescent screen 
must be swept over the face of the tube so as to scan the whole rec- 
tangular area of 7 X 8 inches in l / 2 4 of a second. This sweeping 
operation is performed by applying "saw-tooth" signals, derived from 
the synchronizing pulses, to two other pairs of plates, at right angles 
to each other between the aperture above described, and the fluores- 
cent screen. The potential of one of these sets of plates is controlled 
at a periodicity of 5760 times per second, and sweeps the beam of 
electrons across the screen from one side to the other in exactly the 
same time that the spot of light from the sending-end lens disk tra- 
verses the film. At the end of the sweep the beam is quickly returned 
to its initial position (by the vertical element of the saw-tooth), 
the signal being reduced to zero during this period by masking the 
edge of the film at the sending end. The potential of the other pair 
of plates is controlled at a periodicity of 24 times per second, which is 
the rate of scanning successive frames. These plates, being at right 
angles to the others, deflect the electron beam downward at the same 
relative speed as the film is moving at the sending end. This re- 
sults in the passage of the spot on the fluorescent screen in lines suc- 
cessively displaced by the vertical height of the spot. After the last 
line has been scanned the spot returns quickly to the top of the tube, 
and a properly timed negative impulse superimposed upon the signal 
reduces its intensity during this travel so as to render the spot in- 

Due to the accurate definition of the spot on the fluorescent screen 
and the freedom from distortion, the bright rectangular field produced 



tf. S. M. P. E. 

corresponding to clear film is of a high degree of uniformity and free- 
dom from visible structure, which permits close inspection of the re- 
ceived image. Because of the close approximation to a rectilinear 
relation between the signal (itself accurately proportional to the 
transmission of the film) and the brightness of the scanning spot, a 
high degree of fidelity of tone rendering is obtained. Pictures pro- 
duced by directly coupling the sending and receiving apparatus were 
gratifyingly close in appearance to motion pictures directly pro- 
jected to the same size. 


Given the satisfactory performance of the signal-generating and 
signal-recovery apparatus, when directly connected to each other, 

FIG. 7. Coaxial cable. 

the task of a transmission system is to reproduce this satisfactory 
performance with the sending and receiving apparatus separated 
from each other by any desired distance. For this to be possible the 
transmission medium must to a high degree be immune to interference 
from extraneous sources of electrical energy; it must be capable of 
transmitting the wide frequency bands involved, without discrimi- 
nation between frequencies; and it must be possible to insure that 
all frequencies are transmitted at the same speed. Failure to meet 
any of these requirements will cause serious distortions in the re- 
ceived picture. 

The coaxial cable, shown dissected in Fig. 7, consists essentially 
of a wire supported by insulators in the middle of a conducting tube. 

* A more extended account of the transmission features is given in Electrical 
Engineering (June, 1938), by M. E. Strieby who was directly responsible for this 
phase of the development. 

Sept., 1938] 



Due to the "skin-effect" high-frequency signal currents are carried 
largely in the outer skin of the central conductor and along the inner 
surface of the outer conductor. Currents caused by high-frequency 
external interference flow substantially on the outer surface of the 
outer conductor, and are therefore electrically separated from the 
signal currents by the intermediate metal of the outer conductor. 
Because of this protection from outside interference it is possible to 











_i ** 












95.5 MILES 










200 300 400 500 


FIG. 8. Attenuation of signal strength in coaxial cable. 

subject the signals to an enormous amplification, and so offset the 
very considerable attenuation of signal strength owing to trans- 
mission losses. 

The attenuation of signal strength in the 95 miles of cable between 
New York and Philadelphia is shown in Fig. 8; it increases with 
frequency to a maximum of about 600 db. at 1000 kc. To compensate 
for this loss, repeaters are placed in the line at intervals of 10 miles. 
These repeaters are designed with proper attenuation equalizers so 
as to amplify the low frequencies less than the high, giving a final 



[J. S. M. P. E. 

very flat transmission characteristic over the entire frequency range, 
as shown in the upper diagram of Fig. 8. A photograph of an actual 
two-way repeater and power supply is shown in Fig. 9. 

A characteristic of wire transmission is the distortion caused by 
different times of transmission for different frequencies; the lower 
frequencies lagging behind the higher. In order that the picture 
details will appear in the same relative position in the reproduced as 
in the scanned picture, all frequencies must be received in closely 
the same time relationship in which they were generated. To assure 
this, delay networks were introduced to equalize the transmission 

FIG. 9. 

Repeater and power supply used on coaxial 

speeds over the whole frequency range. The phase delay in the 
coaxial circuit as a function of frequency is shown in Fig. 10, and in 
the upper diagram a measured performance characteristic after the 
delay equalization. 

As discussed earlier the coaxial cable does not offer sufficient 
shielding for very low frequencies, so that the original television 
signals must be translated upward in the frequency spectrum before 
transmission in order to raise them above the region of disturbance. 
The most efficient use of the frequency band available is obtained by 
using only one of the two side-bands normally produced in this 
translating process. In order to place the translated signal in the 
most advantageous frequency position, a double-modulation process 
was used which can be followed with the help of Fig. 11, in which are 

Sept., 1938] 



shown the two modulating steps at the sending end and the two 
demodulating steps at the receiving end in four lines beginning at the 
top. A carrier of 2376 kc. is used for the first modulation, which 
results in a lower side-band from 1570 to 2376 kc. and an upper side- 
band from 2376 to 3182 kc. The carrier itself is eliminated in the 
balanced modulator. The output of this modulation is passed 
through a filter, but because the two side-bands touch each other at 
2376 kc., the filter can not be designed to cut off all the upper side- 





5 550 


g 540 





_ * 







^ * 





95.5 MILES 








S ( 


60 100 200 500 1000 


FIG. 10. Phase delay in coaxial circuit. 

band. At the output of the filter there is thus the lower side-band 
plus a small amount of the lower part of the upper side-band. The 
upper side-bands from all subsequent modulations are readily elimi- 
nated by the filters which follow because of the wide separation. 

The carrier for the second modulation is 2520 kc., and the lower 
side-band extends from 950 down to 144 kc. and for a vestigial range 
below 144 kc. equal to the width of the side-band remaining from the 
first modulation. The high-pass filter following this modulation is 
accurately designed to pass with controlled attenuation not only a 
group of frequencies just above 144 kc. but also the vestigial side- 
band, which extends from 144 to about 120 kc. The resulting signal 



[J. S. M. P. E. 

extending from 120 to 950 kc., is then passed over the coaxial cable 
to Philadelphia. 

Here the transmitted band, after first passing another high-pass 
filter, is applied to the first demodulator, together with a carrier of 
2520 kc.; and the lower side-band, from 2400 down to 1570 kc., is 
passed to the second demodulator where a carrier of 2376 kc. is ap- 
plied. The lowest frequency of the lower side-band, 1570 kc., is 
converted to 806 kc., becoming the highest frequency of the final 



i \T" SIDE-BAND""^ 

v '^' :--' : .': :':':.': f('-'-:{ N^-'^^:::^;;:^^ ! 

3 806 1570 2376 (CARRIER) 3 ' 82 


^J^^J&^ , 

2520 (CARRIER) 


U-_ -UPPER >J 


2376 (CARRIER) 


FIG. 11. Modulation processes used in transmitting broad frequency 
band over coaxial cable. 

demodulated band. The frequencies from 2352 to 2400 kc. of the 
side-band entering the second demodulation had been attenuated 
somewhat by the high-pass filters following the second modulator 
at the sending end and preceding the first demodulator at the re- 
ceiving end; and the second demodulating carrier, 2376 kc., falls in 
the middle of this attenuated band as shown in inset No. 1. Fre- 
quencies extending about 24 kc. above the carrier are inverted by the 
demodulation, and superimposed upon the corresponding frequencies 
just below the carrier. The magnitude and phase of these compo- 
nents are proportioned by the high-pass filters and an equalizer so 


that the overall result, when they are superimposed, is an essentially 
flat transmission band from to 806 kc. 

The terminal equipment, besides providing modulators, ampli- 
fiers, filters, and equalizers, must provide also for the generation of 
the two modulating carriers accurately spaced. This is accomplished 
by deriving all carriers from a 4000-cycle reference frequency at the 
transmitting end. From this source a 72-kc. frequency is first ob- 
tained, and is then used for deriving the modulating carriers of 2376 
and 2520 kc. through harmonic generators. The same 72-kc. fre- 
quency is also transmitted over the coaxial line to Philadelphia, 
where exactly synchronous carriers are derived from it for demodulat- 









I I 



FIG. 12. Utilization of frequency band available. 

Picture synchronization at the two ends is provided by transmit- 
ting a simple sine- wave signal derived from the sending-end scanning 
disk as previously described. This is used to generate saw-tooth 
sweep impulses for the receiving end cathode-ray tube. The 5760- 
cycle synchronizing frequency produced by the disk is modulated 
with the 72-kc. carrier frequency and transmitted as a single fre- 
quency of 66.24 kc. to Philadelphia, where it is demodulated with the 
same 72-kc. carrier to recover the original 5760-cycle synchronizing 

A program channel from 72 kc. to 84 kc. is also provided in the cable 
to accommodate the sound accompanying the motion picture signal, 
and finally frequency space is provided for an order-wire talking 
channel from 60 kc. to 64 kc. and two pilot frequencies at the ex- 
treme ends of the transmitted band, namely, 60 kc. and 1024 kc. for 
automatically maintaining a constant overall transmission level. 

The total television transmission band is indicated diagrammati- 
cally in Fig. 12 which shows that of the total transmitted band of 

272 H. E. IVES 

1024 60 = 964 kc., the actually useful part is approximately 820 
kc. or 85 per cent. 

The terminal apparatus and the coaxial line, as above described, 
were used in a series of demonstrations to interested experts, the 
motion picture film passing through the apparatus in New York pro- 
ducing motion pictures in Philadelphia. It was the generally ex- 
pressed opinion that the pictures seen in Philadelphia were sub- 
stantially the same as those produced by the directly connected termi- 
nal apparatus in New York. On critical examination some transients 
and faint ghosts were detectable in the Philadelphia picture. These, 
however, were comparable with similar defects on the monitoring 
receiver at the sending end, traceable to known characteristics of the 
modulating apparatus capable of improvement; hence are not charge- 
able to the cable system and once located are capable of elimination. 
The experiments have proved that a wide band signal of the type re- 
quired for television can be satisfactorily transmitted over a coaxial 
system. Work is now under way on repeaters and terminal appara- 
tus for transmitting wider bands of frequency to meet the standards 
now being attempted in television. 


R. M. EVANS** 

Summary. By a series of simple assumptions that do not appreciably depart 
from current practice, it is shown that it is possible to calculate readily the concentra- 
tion of any ingredient present in a continuously replenished developer solution during 
use. The equations for the equilibria and rates of growth of the various substances are 
derived, and applied to a practical case. The benefits of chemical analyses for de- 
veloper constituents both for maintenance of quality and for economy are pointed out. 
The analytical methods published by Lehmann and Tausch are outlined briefly. 

In handling motion picture film on continuous processing machines, 
or roll films on intermittent machines, it becomes essential that the 
developer should always have the same properties, not only from hour 
to hour but from month to month. This is true largely because it is 
not economically practicable to vary the time of development to any 
great extent, or to alter the amount of exposure given the material 
in order to compensate for changes in developing power. A single 
reel of motion picture negative may be printed from three to five 
hundred times over a period of a week or more and then be printed 
spasmodically as orders are received over a period of years. To 
change the printing exposures from day to day would be much more 
costly than proper maintenance of the bath. Variation in the bath 
also would not permit the maintenance of consistent quality. 

Accordingly, the larger motion picture laboratories are confronted 
with the problem of maintaining their developers at a constant level 
at all times. Since, from the nature of the problem, replenishing 
must be continuous, it is apparent that the situation is relatively 
complex. It is possible, however, to reduce the problem to a rela- 
tively simple mathematical equation and deduce from this certain 
important rules for procedure. Because of the lack of previous 
literature on the subject the following discussion is relatively complete. 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 20, 1938. Communication No. 673 from the Kodak Research Laboratories. 
** Eastman Kodak Co., Rochester, N. Y. 


274 R. M. EVANS [j. s. M. P. E. 

It should be stated at the outset that nothing short of complete 
running chemical analyses of the solutions and a frequently modified 
replenishing formula is possible for a complete solution of the problem. 
These extremes are seldom necessary because of the variations that 
may be permitted and the possibility of photographic tests. To the 
writer's knowledge such chemical analyses are not at the present time 
being carried out in any of the major laboratories, although the im- 
portance of the problem and the possibilities for economy would 
seem to make them distinctly desirable. 

Maintaining a solution constant involves correcting for variations 
caused both by air and by silver halide. Both these are oxidizing 
agents and their effect varies to some extent with the nature of the 
developing agent. Lehmann and Tausch 1 ' 2 ' 3 ' 4 have shown that 
when an alkaline mixture of elon and hydroquinone is oxidized by 
air, only the hydroquinone reacts. Only after the hydroquinone is 
nearly used up does elon take any appreciable part in the reaction. 
The chief product of the oxidation is hydroquinone monosulfonate, 
which is formed according to the following equation. 

C 6 H 4 (OH) 2 + 2 + 2Na 2 S0 3 = C 6 H 3 (OH) 2 .SO 3 Na + Na 2 SO 4 + NaOH 

The equation for elon is the same except that elon monosulfonate is 
formed. A small percentage of the oxidized developer does not form 
the monosulfonate but passes on to more complex structures. The 
end-product of this small percentage is a brown compound or mixture 
of compounds of the humic acid type. It is this portion of the oxida- 
tion products that causes the familiar stain of severely exhausted 
developers. It appears that not more than 5 per cent of the oxidized 
developing agent passes into this form. 

When an MQ developer is oxidized by silver bromide, however, as 
it is in the normal process of developing an image, it is not the hydro- 
quinone but the elon that plays the more important role. Under 
most conditions there is probably a considerable amount of hydro- 
quinone also oxidized simultaneously. The equation is 

C 6 H 4 (OH) 2 + 2 AgBr + NajsSOa = CeHaCOH^.SOgNa + 2Ag + NaBr + HBr 

for hydroquinone and a similar equation exists for elon. 

Extended oxidation by air or silver bromide will produce consider- 
able quantities of the disulfonates of both hydroquinone and elon 
but since such badly oxidized solutions are not in use they need not 
be discussed here. 


Elon monosulfonate may be used as a developing agent, as was 
pointed out by Tausch, and hydroquinone sulfonate as a developer 
has been known for many years. Both these compounds, however, 
are very weak in their action and their presence in an MQ developer 
in small quantities produces no appreciable change in the bath. To 
the extent that these compounds form in any given solution, they 
may be considered simply as so much hydroquinone or elon removed. 
Some of the other products formed are not at all negligible and are 
considered below in detail. 

The present discussion will be restricted to elon-hydroquinone 
developers that have in their original formulas only sulfite, alkaline 
salts, and soluble halides, in addition to the developing agents them- 
selves. In order to generalize the problem the specific nature of the 
alkali will not be assumed. 

Accordingly, in a fresh batch of developer solution there are 

(1) Elon 

(2) Hydroquinone 
(5) Sodium sulfite 

(4) Alkaline salts 

(5) Soluble bromide (usually potassium) 

Oxidation of this solution by air will produce 

(6) Hydroquinone monosulfonate 

(7) Sodium sulfate 

(8) Free hydroxide (NaOH) 

(9) Staining developer by-products 

Oxidation by silver bromide emulsions (which always contain a 
small percentage of silver iodide) will produce in addition 

(10) More soluble bromide 

(11) Soluble iodide up to equilibrium with the film 

(12) Elon monosulfonate 

(13) Slight traces of elon and hydroquinone disulfonates 

(14) Free acid (HBr) 

(15) Temporary (up to a few hours after use) concentrations of unreduced 
dissolved silver complexes. 

The alkaline water solution will produce 

(77) Dissolved gelatin 

(18) Probable degradation products of gelatin 

276 R. M. EVANS [j. s. M. p. E. 

In addition there will be a gradual accumulation of substances 
present in the emulsion of the film that dissolve out into the developer. 
Such substances are sensitizing dyes (in negative materials), more 
soluble bromide, etc. Dirt, calcium carbonate, and extraneous matter 
will also enter the tanks either on the film or in the water and there 
are probably small amounts of other substances produced by chemical 
reactions of which there is at present no knowledge. 

The problem of replenishing such a solution is two-fold. Starting 
with fresh solution the bath must be brought to a state of dynamic 
equilibrium with film, air, and replenisher, without permitting the 
photographic properties to change appreciably. This equilibrium 
must then be maintained in the face of changing conditions and, in 
general, with only the replenisher as an independent variable, since 
film and air quantities can not be varied at will. In a large industrial 
laboratory the amount of solution in the machines may approximate 
10,000 gallons and the amount of film to be processed may be from 
five to ten million feet of motion picture positive per week. Corre- 
spondingly lower figures hold for negative handling. 

It is customary to connect batteries of developing machines by a 
system of piping in such a way that all the developer may be made to 
circulate past a single point. The volume of the solution is, of 
course, held constant. 

Dry film passes into the developer at a constant rate during the 
operation of a machine and carries with it a small amount of air, 
both on its surfaces and in the perforations. The latent image on 
this film enables the developer to reduce to metallic silver a quantity 
of silver halide that varies widely, depending upon the nature of the 
subject matter. Motion picture positive film contains per thousand 
feet, roughly fifty grams of metallic silver in the form of halide salts. 
Of this, amounts varying from practically none up to nearly the full 
amount may be developed, depending upon the subject of the reel. 
Thus, sound-track or black titles on a clear ground may represent 
only a few grams of silver per thousand feet, while a reel consisting 
largely of night scenes and the like may represent forty grams or 
more of reduced silver. On the average, approximately one quarter 
of the silver is ordinarily utilized or from 10 to 15 grams. The 
remainder may be recovered by an efficient hypo recovery system. 
With respect to a given developing machine, however, the total 
average amount of silver reduced per day is not constant unless care 
is taken to vary the type of work being handled. With an efficient 


circulating system, good mixing, and several developing machines 
operating simultaneously, satisfactory averaging of the work on all 
machines is possible. 

The wet film after development passes out of the developing solu- 
tion into the rinse water, carrying with it a considerable quantity 
of the solution. This quantity varies with the speed of the film, 
the design of the machine and the efficiency of such devices as may be 
present to prevent "carry over." If the surface of the film carries no 
surplus layer of liquid there is in the gelatin of motion picture positive 
approximately one quart of solution per thousand feet. High speed 
and absence of devices to remove the surface layer may triple this 
figure. This solution loss, then, represents a definite minimum 
quantity of liquid that must be added to the system as a whole to 
maintain its volume constant. This quantity frequently is in- 
sufficient and more must be bled away so that the desired amount of 
replenisher may be introduced without overflowing the tanks. 

Since there is seldom occasion to refill such a system completely 
with entirely fresh solutions, the dynamic equilibrium that must be 
maintained after aging will be considered first. Since fresh re- 
plenisher is constantly entering the system, and developer that has 
nearly the photographic properties of the bath as a whole is con- 
stantly leaving the system, considerable economy can be effected by 
choosing the proper position for the point on the system at which 
the two occur. They should be so situated that the "bleed" by 
which solution is removed occurs in the system just before the point 
at which the replenisher enters the system. Theoretically, some 
economy could be effected also by having the fresher developer at 
the end of the machine into which dry film is being fed and the 
more exhausted developer removed from the other end. This sets 
up an unstable balance, however, which breaks down when the ma- 
chine is stopped and so leads to variations over which there is little 

If the system is so designed that perfect mixing may be assumed 
at all times, an equation may be written for the growth or decrease 
of any constituent of the solution. For convenience in computation, 
the figures will be given in the metric system for 10,000 gallons of 
developer replenished at a rate of 2 1 /% gallons per minute. If: 

b = replenisher rate in liters per minute = bleed rate 

v = total volume of the system in liters 

a' = initial total amount of a given substance 

278 R. M. EVANS [j. s. M. p. E. 

x' = amount of the given substance at time t 
k' = amount of the substance added per minute 

then k'dt - b x'dt = dx 1 or ft = ^L 

*' - b -x' 

this equation has as a solution 

. (*'-;') *< , 

'~ 5 >-H r '*~ 

A rather obvious axiom which greatly simplifies the calculations 
may be stated as follows. A substance that, is being formed in the 
solution at a constant rate may be considered as being introduced in the 
replenisher. Since material is also actually added in the replenisher, 
it is convenient to convert the above equation to concentrations rather 
than amounts. Set 


k = = concentration of material in replenisher 


a = = initial concentration of the material in the system 

x = = concentration of the material in system at time / 


The equation may now be converted to these variables, giving, as 
a final solution, 

x = k - (k - a) e~* 

This equation holds for the growth of the concentration of any 
substance in the solution whether the initial value is zero or finite. 
An example will make its application clear. If the initial concentra- 
tion of potassium bromide is assumed to be one gram per liter then 
o=l. Other figures may be assumed as follows: 

b = 10 liters per minute 
v = 40,000 liters 

If several high-speed developing machines are all in operation on 
the system the amount of film developed may be 1000 feet per minute. 
From this quantity of film we may expect that bromide in amount 
equivalent to about 15 grams of silver will be released. This is 
roughly the equivalent of 15 grams per minute of potassium bromide. 
Since complete mixing has been assumed, this amount may be con- 


sidered for convenience as entering in the replenisher, which of itself 
would contain none. This gives k = 1.5 g./liter of replenisher 
solution per minute. 

The equation for x, the concentration of bromide in the bath as a 
whole at time t, becomes : 

-i- * 
x = 1.5 - (1.5 - 1) 4 

or x = .1.5 - 0.5e~ 4000 

Since such a system if operated long enough will come to equi- 
librium at a constant concentration of bromide, it is of interest to 
determine what this equilibrium concentration is. Substituting 
/ = oo it is seen that the last part of the expression becomes zero and 
x = 1.5 grams per liter of potassium bromide. That is, the bromide 
has increased to the concentration calculated above by dividing the 
amount formed per minute by the number of liters per minute of 
replenisher added. This illustrates the fact that the equilibrium 
concentration of all ingredients except those used up in the process 
(developing agents and sulfite) tends to become equal to that of the re- 
plenisher solution. 

It is instructive to consider the time taken to attain this equi- 
librium. Because in theory the limit is approached exponentially it 
is possible to determine only the time required to attain a given 
percentage. For practical purposes 1.45 grams per liter of bromide 
is certainly indistinguishable from 1.50. To find the time required 
to reach this value (97 per cent of equilibrium) it is convenient to 
rewrite the equation so that it gives / in terms of x. That is : 

Under the above conditions then 

t = ^2.3X40,000)1 (1.5 - 1) 

[_ 10 J (1.5 - 1.45) 

and t = 9200 minutes or a little more than six days of continuous 

The mixing in the above example has been assumed perfect. In 
general, if the inlets and outlets are properly placed, the time taken 
would tend to be less than the above rather than more. If there is a 
considerable amount of liquid carried over by the film it may be as- 
sumed that this liquid is somewhat richer in bromide than the solu- 

280 R. M. EVANS [j. s. M. p. E. 

tion in general. In this case the amount of bromide removed per 
minute is greater than that assumed and the equilibrium concentra- 
tion is somewhat less. The time taken to reach the same percentage 
of equilibrium remains the same. 

An exception was made in the application of these equations to 
calculations of the developer and the sulfite that are being exhausted. 
If the replenisher is so increased in the concentration of these ingre- 
dients (above that used in the fresh mix) that the amount used up is 
exactly equal to the amount added there will obviously be no change. 
If under the above conditions 15 grams of silver are reduced, then 
from the equation for the chemical reaction given earlier, the amount 
of developer used up would be approximately 7 grams if it were all 
hydroquinone and 12 grams if it were all elon (one mol of developer 
reduces two mols of silver bromide) . In a positive type of developer, 
we may assume that approximately ten times as much elon reacts 
as does hydroquinone, although this figure must be determined for 
every formula and for every developing time. If this figure is as- 
sumed, then 0.63 gram of hydroquinone and 10.9 grams of elon 
are used up per minute. These amounts must be supplied by the 
replenisher. If the rate of supply of the replenisher is 10 liters per 
minute, then 0.063 gram per liter of hydroquinone and 1.09 grams 
per liter of elon must be present in addition to the amount present in 
the regular formula. By the same reasoning 0.8 gram per liter of 
anhydrous sodium sulfite is needed but such a small amount may be 
neglected . 

The foregoing calculations do not include the effect of air upon the 
solution. It has been shown that this affects only the hydroquinone 
and the sulfite and it obviously depends to a very large extent upon 
the system itself. Variable sources of air are the pumps, the speed 
of the film, the free air surfaces, etc. If it is assumed, for illustration, 
that the entire system absorbs and reacts with the oxygen in one 
cubic foot of air per minute, then the hydroquinone equivalent of 
this oxygen equals 27.2 grams per minute (760 mm. pressure and 
20 C). The sulfite equivalent is roughly 62 grams. Replenishing 
at the rate of ten liters per minute, therefore, it would be necessary 
to add 2.7 grams of hydroquinone and 6.2 grams per liter of sulfite 
in addition to the amount necessary to compensate for development 
of the films. Note that this is for only one cubic foot of air absorbed 
per minute in a ten thousand gallon system. Figures that would 
show the true extent of aerial oxidation in such a system are not 


available. It is apparent, however, that it is economical to go to 
some lengths to reduce aeration of the solution. 

Digressing for a moment it should be noted that the Lehmann and 
Tausch equations quoted 1 ' 2 ' 3 ' 4 above indicate a way in which the 
actual air absorption may readily be measured. Sodium sulfate is 
formed only during aerial oxidation. This product does not appear 
when silver halide is the oxidizing agent. After a bath has been in 
operation for some time and has come to equilibrium with respect to 
this sulfate a simple analysis will give its concentration in grams per 
liter. By the reasoning used above, this quantity multiplied by the 
replenisher rate in liters per minute gives the average amount of 
sulfate produced per minute by the air. One mol of O 2 produces one 
mol of sodium sulfate to a good first approximation. Since the 
ratio of the molecular weights is roughly 4.5, the grams per minute 
of sulfate divided by this figure gives grams of O 2 per minute. One 
cubic-foot of air at 760 mm. pressure and 20C contains 7.9 grams 
of O 2 . Hence, the grams of oxygen per minute divided by 7.9 gives 
the number of cubic-feet of air absorbed per minute. The impor- 
tance of obtaining this figure in such a way that is is accurately aver- 
aged over a considerable length of time is obvious. 

The equilibrium concentration of any ingredient as well as its con- 
centration at any time after the start of the system may be cal- 
culated by the methods already outlined. If the initial concentra- 
tion a of a compound is zero, as in the case of the sulfate, for example, 
the equations are simplified to 

x = kl - e 


where the letters have the same significance as before. The time 
taken to reach 90 per cent of the equilibrium concentration does not 
change since it depends only upon the ratio b/v, of replenisher to total 

It is now possible to consider the problem of starting with a fresh 
bath and bringing it to equilibrium without serious change in its 
photographic properties. The principle involved is apparent. For 
all the ingredients that are of importance it is necessary only that the 
original formula contain the equilibrium amounts desired and that the 
replenisher formula be correct. Under these circumstances, there 
will be no change in coming to equilibrium. These equilibrium 

282 R. M. EVANS [j. s. M. P. E. 

concentrations may be calculated easily since for all cases they are 
equal to the amounts of the substances formed per minute divided 
by the liters per minute of replenisher to be supplied to the solution. 
The elon, hydroquinone, and sulfite concentrations of the original 
solution are arbitrary, but a correct replenisher must contain the 
same amounts plus the amount per minute to be used up in the 
machine. The total alkali concentration must be the same in both 
cases except that since hydroxide is released by air oxidation, and 
silver halide oxidation releases acid, either acid or hydroxide, re- 
spectively, must be added to the replenisher if the rate of production 
of the one during use of the bath exceeds that of the other. The 
addition should preferably be in the form of sodium hydroxide or 
hydrochloric acid so that the alkaline salt equilibrium of the solution 
is not upset. Silver iodide in infinitesimal amounts may have to be 
added. Antifoggants present in used developers may call for the 
addition of small amounts of antifoggants to fresh solutions. 

It is important to note in this connection that the alkalinity of the 
bath at equilibrium can not be calculated by the equations given here. 
It can, however, be held at that of the original mix. When free acid 
or hydroxide is added to a complex solution such as is used for de- 
velopers, the change in alkalinity or H of the solution depends more 
upon the nature and concentration of the compounds present than 
upon the amount of the acid or alkali added. It is entirely possible 
to calculate the amount of hydroxide formed by air (from sulfate 
determinations) and the acid released on development (from bromide 
analyses) and to correct for these by acid or alkali in the replenisher. 
Measurements of H will show whether or not excess has been added 
by indicating a change in alkalinity, although the measurements must 
be very precise if they are to be of value. In general, however, pH 
measurements can not be used to calculate the amount it is necessary 
to add unless careful calibration of the particular solution has been 
made in these terms. 

While some assumptions have been made in arriving at the equa- 
tions above, the only serious discrepancy to be expected is that due to 
incomplete mixing in the machine. This can be estimated satis- 
factorily only for a given system. A further assumption has been 
made; namely, that air and silver oxidation are always present 
simultaneously. In systems in which it is customary to circulate 
the solutions for a long time before film is started this difference must 
be taken into account. For this problem there seems to be no com- 


plete solution except a different replenisher formula for each condition. 

It is now practical to consider the economic phase of the problem. 
The factor that determines the concentration of all the products has 
been shown to be the replenisher rate. If a definite complete formula 
for the bath is prescribed and can not be altered, this is where the 
matter stops; there is only one replenisher formula and one re- 
plenisher rate possible. Assume for instance, that the formation of 
bromide is the most important reaction and the original formula 
which is not to be changed contains 0.5 gram per liter of this sub- 
stance. Then if 15 grams per minute are formed by the development 
of the film, the replenisher rate for the system must be 30 liters a 
minute regardless of its size. The formula of the replenisher is then 
fixed by the amounts of substances, such as developers, that are used 

The determination of the machine formula that will give the most 
economical operation is quite another matter. Certain things are 
readily determined. Since as many liters are thrown away as are 
supplied, the formula should be as dilute as possible in all its original 
constituents except bromide. Since the permissible concentration of 
reaction products formed determines the replenisher rate, the equi- 
librium concentration of these should be high. From this point on, 
the cost of the individual chemicals becomes important and a great 
many questions of quantity against cost and photographic quality 
arise. The answers to these questions will vary so much with in- 
dividual conditions that no direct general solution is possible. A 
few of the opposing facts may be noted. Alkali is cheaper than de- 
veloping agent and so should be high in quantity so that developing 
agent may be reduced. Too high a pH value and too little developer 
gives high sensitivity to bromide and interferes with picture quality. 
High H also usually increases the rate of air oxidation. Sulfite is 
cheaper than hydroquinone but not enough so to warrant using very 
large quantities. Larger quantities confer upon the bath only slightly 
better keeping qualities than do reasonable amounts. Hydroquinone 
is cheaper than elon but the two are not entirely equivalent photo- 
graphically, as we have seen. The solution should be as dilute as is 
permissible. Too great a dilution, however, introduces a large 
difference between the main bath and the replenisher. This in turn 
accentuates circulation nonuniformities and makes a bad situation 
if any of the main body of the solution is lost through leakage. In 
the absence of other considerations the longer the time of develop- 

284 R. M. EVANS [j. s. M. p. E. 

ment and the higher the temperature the more efficient becomes the 
utilization of the developer. Limits are obviously set by the size of 
the machine, by aerial oxidation, and by the physical properties of 
the emulsion gelatin as well as by photographic standards. A high 
degree of agitation of the developer at the surface of the film is de- 
sirable for uniformity, and considerably increases the efficiency of 
the bath. A saving by this means is not to be expected because 
there is a tendency toward excessive aeration. Considerable heating 
of the solution also puts an extra load upon the cooling system. 

It is true in most cases that the greatest possibility of effecting 
economy and at the same time making quality more uniform lies not 
so much in the use of any of the above devices as in obtaining knowl- 
edge of the exact status of the bath at equilibrium. With this 
knowledge it is possible to calculate the correct minimum amount of 
replenisher that may be added and the formula of the weakest re- 
plenisher that may be used. 

Nothing has as yet been said concerning methods by which the 
concentrations of the components of the bath may be checked. 
Such routine tests should be considered a matter of necessity. In- 
crease in aeration alone, due to the sudden leaking of a pump or to a 
similar cause may throw the developer badly off standard. Photo- 
graphic tests have, to date, been nearly the only ones available. 
These are usually satisfactory (except for the time element) but leave 
two important possibilities unmeasured. In the first place, until 
very recent years, there has been no method for checking gradual 
changes since there has been no way of knowing whether the film or 
the developer has changed. The present constancy of motion picture 
positive film characteristics has practically eliminated this problem. 
Second, it is entirely possible, and, in fact likely, that if the formula 
for the replenisher is varied to keep the photographic properties con- 
stant, there will be a progressive change in both the photographic 
quality (as distinct from gamma and speed) and in the composition 
of the bath. Sudden shifts in the quantity of oxygen absorbed by the 
system may vary the hydroquinone concentration greatly. A sudden 
leak in the system, if the latter is of the constant-level automatic 
replenishing type, will introduce large quantities of replenisher un- 

In order to guard against these contingencies and to make certain 
that no large changes are taking place unintentionally, some sort of a 
chemical analysis should be made for all the photographically active 


constituents. The following analytical scheme, abridged from the 
articles of Lehmann and Tausch and the Tausch thesis already re- 
ferred 1 ' 2 ' 3 ' 4 to represent a workable system. Much simpler and 
faster methods must be devised before analytical methods can be- 
come generally applicable. (The hydroquinone analysis given be- 
low is a modification by Lehmann and Tausch of the method of 
Pinnow. 5 ) 

To determine the concentrations of elon and hydroquinone use is 
made of two facts : First, since the oxidation products for the most 
part are the monosulfonates of the compounds, they are not ex- 
tractable from water solutions by immiscible organic solvents such 
as ether. Second, while hydroquinone may be extracted quanti- 
tatively from water if the solution is acidified, this is not true for elon 
since it forms acid salts. Elon may be quantitatively extracted only 
in mildly alkaline solutions (pH approximately 7.6). At this pH 
hydroquinone is also extracted so that it is necessary to remove the 
hydroquinone first. 

The procedure used by Tausch was as follows: 35.7 cc. of de- 
veloper solution was acidified with sulfuric acid to the point where 
a few cc. of hydroxide would again make the solution alkaline (per- 
manent blue coloration of Congo red paper). The released CC>2 and 
SO2 were removed by evacuation. A few drops of methylorange solu- 
tion were added and the whole made up to 50 cc. ; 35 cc. of this solu- 
tion was then extracted with peroxide-free ether for 45 minutes and 
the ether solution separated. The acid water residue containing 
the elon was then made alkaline using methyl orange as indicator. A 
further extraction (20 cc. of ether) for 45 minutes removed the elon 
quantitatively. After evaporation of the ether the two compounds 
were then titrated with iodine in water solution containing sodium 
bicarbonate. From the iodine used up the amounts of the agents 
were calculated for each case. 

To determine the sulfite concentration a modification of well known 
methods was used. A weakly acidified iodine solution (100 cc.) con- 
taining an excess of iodine was placed in a flask and 2 cc. of developer 
was accurately introduced. After a short time the solution was back- 
titrated with thiosulfate to the starch iodide end-point. 

Alkali was determined by titration with acid. Sulfate was deter- 
mined by precipitating with barium salt and weighing the precipitate. 
Soluble bromide was obtained in the same manner after precipitation 
with silver. 

286 R. M. EVANS 

By means of these tests it is possible to gauge accurately the proper 
rate of replenishment and the proper constitution for the replenisher. 
In addition, measurement of pH would give a still further check on 
the state of affairs in the bath. It can not be overemphasized, how- 
ever, that all these tests taken together do not specify the photographic 
quality of the product. They insure merely that the strength of the 
developer does not change. Sulfide-forming bacteria causing fog, 
by-products of development giving stain, and loss of quality from 
other sources must be guarded against by an expert capable of 
recognizing small changes. The present analysis is satisfactory for 
first-order control only. As has been pointed out, however, the re- 
plenisher calculations hold for any product that is continuously 
formed in the bath. For this reason accurate determination of one 
product makes it possible to calculate the others at once. 


1 TAUSCH, E.: "Zur Chemie der photographischen Entwickler," Dissertation, 
Berlin, 1934. 

J LEHMAN, E., AND TAUSCH, E. : "Zum Chemismus der Metol-Hydrochinonent- 
wicklung," Phot. Korr., 71 (Feb., 1935), No. 2, p. 17; 71 (March, 1935), No. 3, p. 

8 SEYEWETZ, A., AND SZYMSON, S.: "Sur les produits d'oxydation des revela- 
teurs organiques," Bull. soc. fran$. Phot., 21 (April, 1934), No. 4, p. 71. 

SEYEWETZ, A., AND SZYMSON, S. : "Influence de la nature et de la proportion de 
1'alcali sur le pouvoir reducteur des revelateurs photographiques," Bull. soc. 
fran$. Phot., 21 (Nov., 1934), No. 11, p. 236. 

4 PINNOW, J.: "Die Sulfurierung des Hydrochinons," Z. Elektrochem., 21 
(Aug., 1915), No. 15/16, p. 380. 

6 PINNOW, J.: "Zur Bestimmung des Hydrochinons," Z.fur Analytische Chem., 
50 (1911), p. 155. 


MR. TOWNSLEY: We have had in our laboratory for the past three years a 
developing machine using continuous replenishment. By a process of cut and 
try, we have arrived at a replenishing solution that works very well in practice. 

We have been able to control both gamma and print density within very narrow 
limits without resorting to changes in developing time or replenishment rate for 
over 18 months. During this time we have processed approximately 25,000 feet 
of 16-mm. film per week. The only control necessary is to compensate for changes 
in sensitivity and developing' rate of film of different emulsion batches. Very 
careful check has been kept on the installation as a matter of engineering record, 
to determine how well stability is being maintained over a period of time, and the 
results have been very gratifying. 


C. M. WERT and L. L. LEWIS** 

Summary. The development and growth of the modern motion picture sound-stage 
has almost paralleled that of sound pictures. Weather, lighting technic, and sound 
recording brought about requirements not originally considered. Modern sound-stages 
have increased not only in quality but in size, and must have structural strength to 
withstand the elements. Sound treatment makes necessary other treatment for satis- 
factory occupancy. Lighting is the greatest contributor of heat within the stage, is 
variable as to amount and duration, and must be controlled correctly. Size and num- 
ber of sets are variable and create individual problems, and both the number and types 
of persons on a sound stage play their parts in relation to the air-conditioning. 

Construction that retards flow of heaj, through walls necessitates control of the heat. 
High-salaried personnel, often in costume, demand comfort while working; less time 
is lost in make-up retouching and less delay brought about by perspiration dampened 

An air-conditioning system should have the ability to heat, cool, ventilate, and 
clean. Stages are generally maintained at 75 F and 50 per cent relative humidity, 
with temperature settings above and below, at the option of the occupants. Floor dis- 
tribution of air has the advantage of more economical removal of rising heat but the 
disadvantage of placing set construction and personnel too near source of cooling. 
Overhead distribution has the advantage of better temperature distribution but is less 
economical in the removal of rising heat from lights. 

Sound treatment of an installation is necessary for continuous operation. If the 
system does not operate continuously the heat load builds up so that the system can 
not adequately regain comfortable conditions during non-shooting periods. Treatment 
is by both isolation and absorption of sound, and can be accurately determined and 

The development and growth of modern motion picture sound- 
stages has almost paralleled the development and growth of sound 
pictures. The addition of sound to action was not the original reason 
for enclosing the spaces where motion pictures are made. Weather 
and the advancement of lighting technic undoubtedly brought about 
the original need for enclosed stages. The advent of sound repro- 

*Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 8, 1938. 

** Carrier Corp., Syracuse, N. Y. 


288 C. M. WERT AND L. L. LEWIS [J. S. M. P. E. 

duction not only increased this necessity, but brought about certain 
additional refinements and requirements not originally considered. 

Size of Stages. Modern sound-stages have increased not only in 
quality but in size. A recent sound-stage, completely sound-treated 
and completely air-conditioned, has been built 316 feet long, 136 
feet wide, and 55 feet high. The floor area of this stage is comparable 
to a football gridiron, and its height to a four-story building. An- 
other recent stage, built primarily to accommodate the tremendous 
sets used in the production of the modern musical revues, has a floor 
area somewhat smaller; but the ceiling of one-half of the stage is 
66Va feet high and of the other half of the stage, 96Va feet. This 
96 Va foot height is impressive and for comparison we must visualize 
an eight-story building. 

Construction of Stages. The construction of the sound-stage 
involves a great deal more than the simple requirement of enclosing a 
space. The entire structure must be engineered to meet code re- 
quirements for earthquake resistance and wind resistance. The 
stage must have a floor capable of carrying heavy rolling equipment, 
large sets, and crowds of people. To eliminate columns the roof is 
of truss construction, designed not only according to the requirements 
of roof construction, but also to provide support for scenery, cat- 
walks and the various braces, wires, etc., that seem literally to infest 
the area above a set. The refinements in the design required for the 
proper reproduction of sound are themselves an engineering problem 
of great magnitude. This paper makes no attempt to go into this 
type of engineering. It is sufficient here to say that the entire stage 
must be sound-proofed against extraneous noises and sound-treated 
for the proper reproduction of sound within. These requirements 
involve the selection of proper materials for the control of sound, 
both as to transmission and absorption. Also, it becomes necessary 
to break the structural continuity of walls, floors, and ceilings to 
minimize the sound-carrying vibrations that originate and progress 
in the structure. 

The floor of the sound-stage, particularly, must not be in rigid 
connection with the wall structure, but must be insulated separately 
to obviate ground noises, such as those produced by passing trucks. 
The result of all these requirements is a structure that may be com- 
pared to an enormously overgrown refrigerator box. The stage, like 
the box, is light-proof, air-tight, sound-proofed, and its construction 
retards the flow of heat in either direction. In this analogy it can be 


seen that the obstructions to the passing of light, air, and heat are all 
intensified by the requirement of a construction necessary for ob- 
structing the passage of sound. 

Stage Lighting. The lighting of a sound-stage is the greatest 
individual contributor of heat gain within the enclosed space. The 
total light load is greatly variable, both as to amount and length of 
time the load is present. The total light load present depends pri- 
marily upon the size of the set upon which shooting is taking place. 
The length of time that the load is present during any one continuous 
period, and the frequency of these periods, are influenced by the 
script, the director, the performers, and the ability of the performers' 
make-up to withstand the effect of the heat produced by the lights. 

In the case of the two large stages previously mentioned, provisions 
were made for 11,000 amperes on the larger stage and 8000 on the 
other. This is equivalent to an average of 28 watts for each square- 
foot of stage area. The concentration of the light is much greater, 
since the area covered by the lighted set is never as great as the area 
of the stage. 

Electricity for the lighting is delivered to the stages in the form of 
direct current. On the large lots this electricity is generated by 
d-c. generators driven by a-c. synchronous motors. These motor- 
generator sets are designed so that the ripples in the d-c. voltage will 
not exceed =*= 1 per cent. Due to the intensity of lighting required, a 
greater variation in voltage would create a change in this intensity 
sufficient to register on the photographic film. 

Due to the heavy intermittent load, which might at times overload 
the feeder to an individual stage, the motor-generator sets are over- 
compounded approximately 6 volts to compensate for the drop in 
voltage due to these overloads. Hard arc lighting requires the use of 
choke-coils to eliminate the sound or whistle created primarily by 
commutator ripple and attenuated by the high frequency generated 
in the arc crater of the lamp. Each arc light also has its individual 

Stage Scenery or Sets. Obviously there is great variation in the 
size and number of sets on a sound-stage at any one time. At times 
the entire stage may be utilized as one large set; at other times, 
numerous smaller sets may be scattered about the stage. These 
sets vary both as to size and type, to such an extent that we might say 
that no two are ever alike. 

Basically, the sets are three-sided and topless. They are stages 

290 C. M. WERT AND L. L. LEWIS [j. s. M. p. E. 

within a stage, and, as such, affect the acoustic conditions of the whole. 
Proper treatment for this situation provides a medium in the con- 
struction of the set that will pass the sound bodily through the set to 
the treated walls and ceiling of the stage proper. Such procedure 
calls for the elimination of all hard-walled sets and the construction of 
sound sets to meet acoustical requirements upon the same basis as the 
stage proper. One of the steps toward overcoming reverberation 
within the confined area of the set itself is the use of dyed muslin 
stretched on wood frames for all smooth- walled sets. 

Sets within the sound stage offer their problems also to the lighting 
engineer and to the air-conditioning engineer who must deliver cooled 
air properly to the area embraced by the set. 

Occupancy of Stages. The motion picture company, like the elec- 
trical power company, sells to the public something that is intangible. 
Motion pictures, through the medium of reproduced light and sound 
depict the emotions and personalities of one group of persons, the 
actors, to another group within whom is created an emotional re- 
action. The technical side of motion picture making requires not 
only a great number of persons, but a great variety of trades and 
personalities. Press agents have given us some idea as to the per- 
sonalities, but it is not as well known that there are some 278 different 
trades and professions in the motion picture industry. At one time 
or another a great number of these are represented on the sound- 
stage, but we shall make no attempt to enumerate or classify them. 

On the large stages previously mentioned, some 400 persons have 
been anticipated and provided for, but this number may be exceeded 
on occasions. A number of the occupants are, of course, actors and 
actresses in costume and make-up. Human occupancy of the sound- 
stage brings with it certain additional problems, some of which we 
must admit can not be solved by the slide rule of the engineer. 

Necessity of Air-Conditioning in the Sound-Stage. All the items 
covered in the general discussion of sound-stages play a part not 
only in the design of air-conditioning systems for the stage but also a 
part in the necessity of air-conditioning. Basically, sound-stages 
are being air-conditioned in one degree or another only because air- 
conditioning has been proved necessary and the results obtained are 
of economical value. 

Necessity as Result of Construction. The refrigerator construction 
of the modern sound-stage, with its capacity for retaining the heat 
generated within it, is a contributing factor to the necessity of air- 


conditioning. The cumulative effects of heat generation must be 
removed if the quality of the stage's availability for continuous use is 
to be of the same calibre as the quality of its construction. No ex- 
pense has been spared to further its ability to keep out light, sound, 
and weather, and this same expense furthers its ability to keep in 
generated heat and vitiated air. The insulating value of the sound- 
stage wall can readily be perceived by considering the construction 
from outside to inside: 1-inch Gunite plaster, metal lath, water- 
proofed paper backing, laminated wall panel containing air space, 
2-inch acoustical rock wool, and 44-40 count flame-proof muslin 
protected with hardware cloth or chicken wire. 

The roof construction is similar in character, although, of course, 
the Gunite is replaced by roofing. Floor construction consists of 
1 X 6-inch T and G finish flooring with 2 X 6-inch sub-flooring, all 
supported on 2 X 10-inch floor joists on 12-inch centers. The floor 
level is 3 to 4 feet above ground level. The sound-stage, with its 
specially constructed doors closed, can be said to be hermetically 

The construction that we have just described covers one of the 
most recent sound-stages. All the sound-stages in use may not be 
typical in construction, but if well-designed, they are typical as 
regards sound and heat transmission. From this can be seen that the 
sound-stage is a structure that does not allow the entrance or exit of 
air, and so retards the flow of heat that practically, if not theoretically, 
there is no flow of heat through the structure. This quality of the 
structure brings into being two requirements met by the air-condi- 
tioning system: (1) The use of air delivered into the stage for actual 
transportation of heat out of the stage; (2) The furnishing of new air 
to meet the ventilation requirements of the occupants. 

Necessity as Result of Lighting. The light load is the most im- 
portant consideration of the engineer in the design of an air-condi- 
tioning system for the sound-stage (Fig. 1). The production of 
motion pictures is based upon light and its proper application. Light 
on the sound-stage is artificial light, and emits heat, most of which is 
in the form of radiant energy that becomes sensible heat as soon as it 
strikes an absorbing surface. So-called cold light, such as that 
produced by the firefly, would be very advantageous. It is possible 
to produce such light by mixing a luminol-caustic soda solution with 
a hydrogen peroxide-potassium ferricyanide solution, but the cost 
is more than a million times as great as the light produced with the 



[J. S. M. p. E. 

modern incandescent lamp. l Even though there may be reports to 
the contrary, air-conditioning is still more economical. 

The air-conditioning engineer has been familiar with the problem 
of lighting and its results for many years. The tendency toward 
increased lighting in commercial establishments has not caught him 
unprepared. Published data on the subject are rather meager, due, 
we believe, to the fact that possibly the "doctor" has recognized 
and treated the disease successfully without finding it necessary to 
determine its degree. The number of pills for the patient has been 





FIG. 1. Diagram of heating element of air-conditioning 

determined by his size and the effect of the pill upon previous pa- 

Sound-stage lighting is a special problem of great magnitude and 
importance. The intensity and amount of sound-stage lighting has 
already been mentioned. Light is produced on the stage by two 
means: (1) incandescent lamps, and (2) carbon arc lamps, each 
having its own characteristics. The carbon arc lamps are required 
for producing intensities beyond the scope of the incandescent lamps. 
On large sets, where light must be thrown for considerable distance, 
there will be a preponderant amount of arc lighting, possibly to the 
extent of three to one. On the average set the ratio of arc to in- 
candescent lighting is closer to unity. All the electrical energy 
brought into the sound-stage for the production of light eventually is 
transformed into sensible heat. Fortunately, all the heat is not 


released in the area occupied by the people, or what is more commonly 
called the "breathing zone." 

Since the size and cost of an air-conditioning system for the sound- 
stage is influenced more by the light load than any other single factor, 
it is imperative that the air-conditioning engineer correctly diagnose 
the effects of this load in order to produce the guaranteed results 
within the breathing zone. Providing refrigeration for the entire 
energy input would be poor economy and, as such, must be guarded 
against by the engineer. Numerous factors influence the engineer's 
calculations regarding the effect of lighting upon the size of the air- 
conditioning system. Some of these factors are: 

(1} Total average maximum load. 

(2} Possible intermittent maximum load. 

(5) Maximum length of time load occurs. 

(4) Frequency of load occurrence. 

(5) Possible maximum concentration of load within the stage. 

(6) Height of the stage. 

(7) Possible ratio of arc to incandescent lamps. 
(8} Reflecting characteristics of material lighted. 
(9) Location of lights. 

The factors just given are largely self-explanatory, but two of them, 
7 and 8, warrant additional explanation. 

As mentioned before, arc and incandescent lamps have certain 
individual characteristics. The gas-filled incandescent lamp oper- 
ated at normal voltage in still air has an energy distribution about as 
follows: 2 


Radiation in the visible spectrum 11 

Heat as invisible radiation in the infrared region 70 
Heat which is conducted away from the filament through the filament 

supports and leads 3 

Heat dissipated by gas convection and conduction 8 

Heat radiation by the bulb 8 

Hence, from a clear bulb, about 90 per cent of the total energy is in 
radiant form; i. e., all except that dissipated by the filament supports 
and leads and by air passing over the bulb. This large amount of 
radiant energy will not be effective in raising the temperature in the 
interior of the stage until it has been intercepted by an absorbing 
surface which, in turn, will dissipate the heat by convection. The 

294 C. M. WERT AND L. L. LEWIS [J. S. M. p. E. 

radiant energy will, however, increase the feeling of warmth to the 
human body by its radiant effect. 

On the sound-stage the aforementioned percentage of energy in 
radiant form is affected, to some extent, by the housing or reflector 
covering the bulb. The greatest percentage of the energy, how- 
ever, is still released in the form of radiant energy. All this energy is 
eventually absorbed by an absorbing surface. The invisible radia- 
tion follows the same path as the visible radiation. It is not all 
absorbed by the first intercepting body but only a certain percentage 
of it, depending upon the ability or inability of the body to reflect it. 

Assuming that it is possible to visualize a single stream of radiant 
energy striking the floor of a stage set at an angle, a certain portion 
of this radiant energy being deflected against the wall of a stage set; 
and in turn visualizing a certain percentage of the energy being de- 
flected upward to the top of the stage, it can be realized that a certain 
amount of this radiant energy is dissipated on surfaces far above the 
breathing zone. 

Arc lights have an entirely different energy distribution. The 120 
volts delivered to an arc light set-up is reduced by resistance to 72 
volts across the arc proper. This means that before the arc is 
produced, 40 per cent of the incoming energy is released in the form 
of heat from the resistor by convection and conduction. Since a 
great number of arcs are used to light the set from above, it can be 
seen easily that arc lighting has a different effect upon air-condition- 
ing design than does incandescent lighting. 

Air-conditioning, as regards the light-heat generation, provides the 
medium for wiping the surfaces exposed to the radiant heat, both 
visible and invisible ; thus increasing the heat removal by convection 
and conduction. It also provides a medium for removing the heat 
not transformed into radiant energy. 

Necessity Due to Occupancy. The fact that the sound-stage is 
occupied is, of course, the basic reason for air-conditioning. It has 
long been necessary to provide some means of ventilation for spaces 
occupied by a group of persons in order that vitiated air might be 
replaced, and of removing heat at a rate depending upon the out- 
side temperature. Certain combinations of various factors resulted 
in comfortable conditions within the space while other combinations 
did not. 

Air-conditioning was first used in the industrial field for producing 
and maintaining predetermined temperatures and humidities, regard- 


less of outside weather. Applying it to public spaces brought forth 
the fact that comfort was a marketable product and that the public 
would patronize more freely spaces that were comfortable. 

The next step was comfort for the purpose of obtaining better re- 
sults from salaried employees. In the sound-stage,' where human 
beings play such an important part in the scheme of things, comfort 
becomes a necessity rather than something to be hoped for. Heavy 
costumes and make-up do not go well with incandescent lamps and 
arcs when the quality of the acting is dependent upon the comfort or 
discomfort of the actors. 

Necessity from Economic Viewpoint. It is doubtful whether the 
actual economic dollar value of air-conditioning on sound-stages has 
ever been calculated. The great number and importance of intangi- 
ble and variable factors would complicate any such calculation to an 
enormous extent. Certain factors are present, however, that are self- 

In the moving picture business, as in other businesses, time spent 
is money spent. Satisfactory results can be produced under com- 
fortable conditions more quickly than under uncomfortable condi- 
tions. Uncomfortable and often unbearable conditions in un- 
conditioned spaces are fought in many ways; doors are opened be- 
tween shots for flushing the stage with air; shots are delayed; ice 
cakes and dry ice are brought upon the stage; shots are made at 
night. All these expedients lead to loss of time and money. Damage 
by perspiration to costume and make-up is one of the obvious factors 
that can easily be seen to have a dollar value. Probably the most 
conclusive evidence of the economic value of sound-stage air-con- 
ditioning is the fact that air-conditioning systems are still being 
installed by companies that have had previous experience with them. 

Application of Air -Conditioning. Complete air-conditioning of the 
sound-stage must meet many requirements. The system must be 
flexible, able at all times to meet the requirement of heat and ventilate 
properly, clean the air, cool, remove smoke and fog, maintain proper 
temperature and humidity within the breathing zone, and properly 
meet various other requirements, each of which presents certain 
problems and points of interest. 

Heating. Heat production on the sound-stage has been so stressed 
that the need for heating the stage by the air-conditioning system may 
not be evident. During the period of set building, before shooting 
can take place, stage doors are thrown wide open. Some of these 

296 C. M. WERT AND L. L. LEWIS [j. s. M. p. E. 

doors are of tremendous size, built for the entrance and exit of large 
pieces of scenery and can accommodate some smaller sets in their 
entirety. Some of these doors are 24 feet high and 18 feet wide. 
California nights are cool, and due to the high ceilings and the re- 
sultant stack action of heated air escaping from exhaust openings, 
the stage tends to fill with cool air, particularly at the lower level. 
If production is due to start in the morning, heat must be supplied to 
produce comfortable conditions for the initial occupancy, even though 
cooling may be required a short time thereafter. Heating, of course, 
is seldom required during the shooting, except possibly on a stage with 
a small set during cold weather and on rehearsal stages where no 
shooting is taking place. 

Due to this tendency of the large stages to fill with cool air, it is 
considered necessary on one large lot to have heat available for nine 
months of the year. 

Ventilation. Ventilation, or the replacement of vitiated air, is the 
oldest function of air-conditioning. Under the artificial conditions 
of indoor life, air undergoes certain physical and chemical changes 
that are brought about by the occupants. The oxygen content is 
reduced somewhat, and the carbon dioxide slightly increased by the 
respiratory process. Organic matter, which is usually perceived as 
odors, comes from the nose, mouth, skin, and clothing. 

The temperature of the air is increased by the metabolic processes 
and the humidity raised by the moisture emitted from the skin and 
lungs. Contrary to old theory, the usual changes in oxygen and 
carbon dioxide are of physiological concern, because they are too 
small even under the worst conditions. Little is known of the 
identity and physiological effect of the organic matter given off in the 
process of respiration. The only certain fact is that expired and 
transpired air is odorous and offensive, and is capable of producing 
loss of appetite and a disinclination for physical activity. These 
reasons, whether esthetic or physiological, call for the introduction of 
a certain minimum amount of clean, outdoor air to dilute the odor- 
iferous matter to a concentration that is not objectionable. 

Ventilation of the sound-stage always exceeds, by many times, the 
actual requirements for comfort of the occupants. This excess 
outside air, over and above that required by the occupants, is brought 
into the sound-stage for the sole purpose of removing the concen- 
trated heat from the upper levels. After it has performed this func- 
tion it is exhausted and discharged again to the outside atmosphere. 


Air-conditioning systems for sound-stages are often designed on the 
consideration that the minimum amount of outside air will be 50 per 
cent of the total fan capacity, or the ability to deliver air to the stage. 
On the large stages designed to hold 400 persons, this minimum quan- 
tity of outside air is sufficient for the ventilation requirements of 
7500 occupants. For conservation of refrigeration during favorable 
outside weather conditions and also for the quick purging of smoke 
and artificial fog, the sound-stage air-conditioning system is always 
designed for the ability to handle 100 per cent of its capacity from the 

Air Cleaning. Air cleaning, or filtering air, requires little explana- 
tion to prove its importance in air-conditioning. The atmosphere in 
all localities contains dirt and dust to some degree. The accumula- 
tion of these particles, even though minute, will eventually interfere 
with the economical operation of an air-conditioning system. The 
beneficial effects of clean air as regards health and comfort are very 
well known. As regards the sound-stage in particular, dust floating 
in air can not be tolerated since the motion picture camera easily 
records it. 

Cooling. The cooling function of an air-conditioning system is the 
function most publicized, and as a result, to the public, the terms 
"air-conditioning" and "cooling" are synonymous. To the air- 
conditioning engineer cooling also means dehumidification, or the 
removal of moisture by condensation; since generally the two func- 
tions, removing heat and removing moisture, are necessary and are 
performed by the same equipment at the same time. 

As regards the sound-stage, cooling and dehumidification are the 
functions of air-conditioning systems that remove, from a predeter- 
mined volume of air, a predetermined amount of heat and moisture; 
so that the delivery of this predetermined volume of air to the sound- 
stage and the absorption by the air of a certain amount of generated 
heat and moisture, will result in a temperature and humidity comfort- 
able to the occupants. 

The heat and moisture present on the sound-stage determine the 
heat and moisture content required of the air delivered to the sound- 
stage. When the temperature and humidity of the outside atmos- 
phere are higher than required for the delivered air, refrigeration 
must be used to produce the results desired. The delivered air is 
cooled either by contact with a fine spray of cold water or by con- 
tact with coiled metal surfaces containing the refrigerating medium, 



[J. S. M. P. E. 

either gas or liquid. Refrigeration is accomplished by either recipro- 
cating or centrifugal type refrigeration machines. 

The intermittent and variable heat load present on sound-stages 
makes the storage type of refrigeration particularly applicable. 
The maximum heat load on the sound-stage is present during the 
periods of shooting, which are variable as to both time and number. 
Sufficient instantaneous capacity furnished by a refrigeration machine 
alone would require a machine of great capacity (Fig. 2). 

A storage type of system combines a large tank or reservoir of 
cold water, and the refrigeration machine. With this combination 
it is possible to use a smaller refrigeration machine operating con- 
























-L J. J 





1 ; 1 1 LINES. 




FIG. 2. Water circulating system. 

tinuously at maximum efficiency. During the period when no shoot- 
ing is taking place the excess capacity of the machine is conserved in 
lowering the temperature of the reservoir of water. During the 
period of shooting, when the heat load within the stage is greater than 
the capacity of the machine, additional cooling is furnished by the 
tank in sufficient quantity to meet the requirements of the heating 
load. A large refrigeration machine meeting the requirements of 
intermittent and variable loads does not compare favorably, eco- 
nomically, with a smaller machine running continuously at maximum 
efficiency. The requirements and total cooling by both set-ups 
are, of course, identical-. 

Exhaust. The construction features that render a sound-stage 
air-tight also lead to the necessity of exhausting air from it. Air 
from the outside is necessary, and unless air be removed from the 


inside, the amount that can be introduced will be limited by the 
pressure-producing ability of the supply fan. When the pressure 
within the stage reaches the limit of the fan's capacity, no more air 
from the outside can enter. The expedient of providing openings 
for relieving the inside pressure is not satisfactory, since this requires 
an internal pressure to force out the air, and the pressure required 
would be increased by the necessity of sound-treating the exhaust 
openings. Pressure inside the sound-stage is objectionable due to its 
effect upon the operation of the doors. An unbalanced pressure on 
the two sides of the large doors will prevent opening them, and inside 
pressure interferes with the proper closing of the smaller pedestrian 

Mechanical exhaust permits maintaining the pressure inside the 
stage equal to the pressure outside the stage, by overcoming the re- 
sistance of the exhaust openings. It permits also the use of smaller 
exhaust openings, which can be more satisfactorily and economically 
treated against sound transmission. Proper location of the exhaust 
openings at the highest level enables the exhaust air to pick up the 
greatest amount of heat and arc light smoke and carry it to the out- 

The capacity of the exhaust system is variable, to agree with the 
ability of the supply system to deliver variable quantities of outside 
air to the stage. For very fast purging of the stage after heavy 
smoke or fog scenes, full capacity of the exhaust system is used, with 
all doors opened and the supply system not in operation. 

Air Distribution. Air distribution on the sound-stage is quite 
important in that the complete success of the system depends largely 
upon the results obtained by the distribution. It is necessary to 
handle large volumes of air to compensate for the heat concentration 
without creating discomfort to the occupants. 

The air-distribution system must be flexible so that extra air may 
be concentrated at any particular section of the stage if desired 
(Fig. 3). Quite often a distribution that is satisfactory for a certain 
number of sets may require alteration for another group of sets. 
The temperature and humidity are important only in the breathing 
zone, and the distribution system should not be arranged in any man- 
ner that would have a tendency to interfere more than necessary 
with the natural tendency of heat to rise and stratify. 

The most economical air-conditioning system, of course, would be 
one that conditions the floor area to a height of only seven or eight 



[J. S. M. P. E. 

feet. Practically, this is impossible, but the air-conditioning engineer 
approaches this ideal as nearly as possible in design, limited only by 
other requirements. Some of the original sound-stages were con- 
ditioned by introducing conditioned air along the side walls and near 
the floor level. The air was delivered at a low velocity, out across 
the floor, where it picked up the liberated heat in the breathing zone, 
rose to the top of the stage, and was pulled away by an exhaust fan. 
This form of distribution really delivered the air directly to the 


/\ /\ 

\ONomoneo AIR X 

l\ l\ 


g^3 G E3 


FIG. 3. End section of sound-stage. 

breathing zone, and very little cooling effect was wasted at the higher, 
unoccupied level. 

Difficulties began to arise when it was found impossible to prevent 
the building of sets and drops directly in front of the supply outlets; 
which, of course, prevented a part of the air from reaching the oc- 
cupied spaces of the stage. Also, occupants having duties other 
than acting often had to be located near the supply outlets; which, 
of course, led to complaints, and rightfully so, since the temperature 
of the air at the delivery points was considerably below the re- 
sulting room temperature after the air had absorbed its heat. These 
objections were intensified by the tendency of the companies to do 
more and more of their shooting inside the stages, with a conse- 
quent increase in the size of the sets and bringing them closer and 


closer to the walls of the stage. It was then the problem of the air- 
conditioning engineer to overcome these objections and still retain, 
in a measure, the original intention of applying the conditioning 
primarily to the occupied space or breathing zone. 

Increased size and variable location of the sets made it inevitable 
that the air must be delivered from above the set. This led to a 
design that would enable delivery of conditioned air downward 
against a blanket of heated air rising upward. The process of adding 
cold water to a tub of water too hot for comfort is well known 
the cold water sinks to the bottom of the tub and forms a cool layer, 
displacing the hot water, which is forced upward. In order to get an 
even temperature it is necessary to agitate and mix the cold and hot 
water. Somewhat the same principle is applied to the downward 
distribution of air. The cool, or conditioned, air is not only heavier 
than the warm air, but it is started in a downward direction by a low 
velocity produced by the supply fan. Cool air actually displaces 
the warmer air and the mixing is accomplished by friction or con- 
tact along the perimeter of the cool air stream. Supply outlets are 
designed to keep the cool air stream as confined as possible for as 
great a distance downward as possible, but also with the purpose of 
reaching the full area of coverage at the top of the breathing zone. 
This distribution can be visualized by picturing a great number of 
slender pyramids hanging by their apexes from the sound-stage roof, 
with their bases touching on all four sides at a level seven feet above 
the floor. All the space above the bases and between the pyramids 
would represent the space through which heated air could rise. This 
final blanket of air at the top of the breathing zone must reach there 
at sufficiently low velocity as not to produce objectionable drafts. 
Reverting to the bath-tub analogy, it must be noted that agitation, 
or mixing, has been guarded against as much as possible. 

The exhaust openings of the sound-stage are located at the roof 
level, and the bottoms of the supply outlets are located at the level 
of the bottom of the truss structure. The air-conditioned sound- 
stage, when in operation, has at the bottom a layer of air in the proper 
conditions; and at the top, air that has been heated. The air at the 
top, during operation, is generally warmer than outdoor air, and also 
contains smoke from the arc lamps. Being worthless, it is discharged 
to the outside atmosphere. 

The conditioned air at the bottom of the stage is often more desirable 
than the outdoor air, and is drawn off at the floor level and returned 

302 C. M. WERT AND L. L. LEWIS [j. s. M. P. E. 

to the conditioning system where it is mixed with an additional supply 
of outside air. To maintain a balance of pressure inside and outside, 
the exhaust system removes heated air from the top of the stage in 
the exact quantity as outside air is added to the system. The quan- 
tities of air supplied to the stage, taken from the outside, and ex- 
hausted from the stage are all manually adjustable from inside the 

Inside Atmospheric Conditions. Although other features might 
possibly influence the buyer's satisfaction, the resulting inside at- 
mospheric condition is the main yardstick for determining the success 
of an air-conditioning installation. Systems are designed for the 
express purpose of producing certain atmospheric results within the 
sound -stage, and it is normally a requirement of the air-conditioning 
contractor to guarantee the production of those results. 

For economic reasons various limitations are placed upon design 
of air-conditioning systems. Extremes of short duration (in occu- 
pancy, lighting load, and outside weather) are not considered; 
especially since several extremes may not simultaneously occur. 
Guaranteed summer cooling requirements in southern California are a 
temperature not exceeding 75 F and a humidity not exceeding 
50%; with outside conditions not exceeding 90F dry-bulb tem- 
perature and 70 F wet-bulb temperature. 

Heating design is generally based upon maintaining a temperature 
of 70F when the outside temperature is not lower than 30F. 
Due to the large volume of the sound-stages, a more important re- 
quirement is sufficient heating capacity to bring up the temperature 
within the stage to the desired point within a stated time, generally 
ninety minutes. 

With present-day knowledge the air-conditioning engineer can 
predetermine the most economical design of a system having the 
capacity to produce guaranteed results. 

Present Air -Conditioned Stages. The history of air-conditioning 
of the sound-stage is almost covered by the past ten years. The 
present tendency toward doing more of the work inside the stages, 
aided considerably by the advances made in using process backgrounds 
will undoubtedly increase the application of air-conditioning to sound- 
stages. At the present time three major companies, namely, Twen- 
tieth Century-Fox, Paramount, and Metro-Goldwyn-Mayer have a 
total of thirty-five air-conditioned sound-stages. 

Application of Sound Treatment to Air- Conditioning. The advent 



of sound reproduction into the radio and motion picture industry 
caused the air-conditioning engineer to take up the study of sound. 
It not only became necessary to provide air-conditioning for broad- 
casting studios and sound-stages without objectionable sound, but 
the advance of sound pictures proved that many existing theater 
installations required treatment and adjustment. The following 
discussion covers the general application of sound treatment of the 

FIG. 4. Detail of supply apparatus (plan}. 

air-conditioning system for the motion picture sound-stage (Figs. 4 
and 5). 

Necessary for Sound Treatment. At first thought there seems to be 
no reason proving the necessity of sound treatment for sound-stage 
air-conditioning systems, since the necessity seems obvious. At the 
present time there are several degrees in the quality of sound treat- 
ment, both on air-conditioned stages and on stages not conditioned. 
In some cases doubtless the requirements became more stringent, 
and left the treatment inadequate. Regardless of the reasons why, 
stages with and without complete air-conditioning can be placed in 
two classes; those on which shooting can take place with the system 



[J. S. M. P. E. 

running, and those on which the system must be shut down. The 
stage upon which the equipment must be shut down of course re- 
ceives no ventilation or cooling during the period of greatest heat 
generation. This form of operation leads to building up the heat so 
that it may eventually get beyond the capacity of the air-conditioning 
equipment to handle it, and on the unconditioned stage leads much 
faster to an unbearable condition. 

Proper sound treatment, correctly engineered, will enable full- 
time operation of the air-conditioning system and not interfere with 
the reproduction of sound. The modern sound-stage is a quality 
structure, designed and built for a specific purpose, and it is only fit 

FIG. 5. Detail of exhaust apparatus (plan}. 

and proper that the air-conditioning system for such a structure 
should be commensurate in quality and ability to perform its duty at 
all times. 

Method of Sound Treatment. The objectionable noises that might 
enter the sound-stage due to the air-conditioning installation may be 
grouped into two classes: 

(1) Noise transmitted through the building construction, such as from ma- 
chine mountings and vibrations, and from equipment through room walls and 
floor surfaces. 

(2) Noise transmitted through air-carrying ducts, such as from fans, from 
outside through duct walls into the air stream, and noise generated by the flow 
of air. 


Noise that might be transmitted through the building structure can 
be taken care of very rapidly. All moving equipment is placed upon 
properly designed isolation supports so that objectionable vibrations 
may be absorbed. Flexible connections are used between moving and 
stationary pieces of equipment. The equipment rooms of sound- 
stages are not only designed to prevent passage of noise from their 
structure, but are located outside the stage. 

Noise transmitted through the air-carrying ducts is not so readily 
overcome. It is impossible to select air-handling equipment for 
air-conditioning that will operate without producing some noise 
that will be carried by the air stream. However, the noise is kept as 
low as possible by properly selecting the equipment, not only as 
regards the amount of noise produced, but as regards the frequency of 
the sound. All duct work outside the sound-stage is insulated to an 
extent equivalent to the stage wall's ability to exclude sound. Noises 
generated by the flow of air are prevented by properly designing 
the duct system and individually treating the parts of the system 
having a tendency to generate noises due to contact with moving air. 

After all the prevention expedients are taken care of by proper 
design, it is possible to calculate the natural absorption of the system 
since all air-conditioning systems using ducts for carrying the air 
have a certain capacity to lower the generated noise level. In sound- 
stage applications the construction of the stage and distance of the 
air openings from the point of reproduction play a part in reducing 
the sound level. The allowable sound level is specified and de- 
termined by the stage reproduction requirements and design. The 
difference in sound level between the allowable level and the calcu- 
lated level of the system determines the additional sound treatment 
that must be applied to the system. Many materials are now rated 
by the manufacturers with sound-absorbing coefficients, and there 
are several methods of application, generally determined by the 
arrangement of the parts making up the installation. 

One part of the treatment generally used in sound-stage condition- 
ing systems is the concentration of the absorbing material at one 
point, in cells or passes through which the air must flow. Plenum 
effects, wherein fans are discharged into large acoustically-lined 
chambers, the discharge velocity being impacted against the walls of 
the chamber, have also proved very effective. 

Space does not permit going into the details and theory of sound 
treatment. Suffice it to state that the required treatment can be 


determined as effectively as other air-conditioning requirements of 
the sound-stage, to the point of making and delivering predeter- 
mined sound level guarantees. 

Guarantees. The following guarantee, made on a recent sound- 
stage air-conditioning installation, points out not only the require- 
ments of the guarantee, but the ability of the contractor to meet these 
requirements : 

"It is agreed that the increase in noise level in any of the six con- 
ditioned stages resulting from the normal operation of the completed 
air-conditioning system shall not exceed a value equivalent to an 
energy level of 29 decibels above an arbitrary established zero sound 
level of 10~ 16 watt per square centimeter over a frequency range of 
30 to 300 cycles, and shall not exceed a value equivalent to an energy 
level of 19 decibels over a frequency range of 300 to 10,000 cycles. 
In all cases the noise level shall be measured at a representative 
microphone location and at a level of five to eight feet above the floor, 
but in no case shall the measurement be taken closer than 5 feet to 
any wall. The equivalent loudness shall be determined from 30 to 
10,000 cycles either by a weighted electrical network or by a hand 
frequency analyzer." 

Acknowledgment. The authors wish to acknowledge their appre- 
ciation of information given to them by J. M. Tobin and C. P. 
Hubert of the Metro-Gold wyn-Mayer Corp., and E. L. Ellingwood, 
Consulting Engineer, Los Angeles, Calif. 


1 STURROCK, W. : "Effects of Artificial Lighting on Air-Conditioning, " Heating, 
Piping, and Air Conditioning, 10 (Feb., 1938), No. 2, p. 134. 

2 FORSYTHE, W. E., AND WATSON, E. M. : "The Tungsten Lamp," /. Franklin 
Inst., 213 (June, 1932) No. 6, p. 623. 


During the Conventions of the Society, symposiums on new motion picture appara- 
tus are held in which various manufacturers of equipment describe and demonstrate 
their new products and developments. Some of this equipment is described in the 
following pages; the remainder will be published in subsequent issues of the Journal. 


New photographic problems have arisen from the introduction of motion pic- 
ture negative films having a greater increase of speed over the prevailing types 
than the supersensitive panchromatic films had at the time of their introduction. 1 
Some of the problems confronting motion picture cameramen and laboratory 
technicians can be considered in the light of solutions that have been evolved by 
theory and practice. 

In general, Ultra-Speed panchromatic film, compared to Superpan negative 
film, is much faster; slightly flatter in gradation; similar in color-sensitivity, 
with slightly greater response to red light; and possessed of a somewhat coarser 
grain. Of these characteristic differences, the speed relationship has the greatest 

The Problem of Correct Exposure. A wide variety of tests made under a num- 
ber of conditions of practical photography 2 have shown that Ultra-Speed pan- 
chromatic film is correctly exposed when given two lens stops less exposure than 
Superpan negative film. Since the principal application of the film tends toward 
those conditions of photography or to cinematographic subjects that have been 
considered difficult to photograph or impossible to record because of insufficient 
illumination (Fig. 1) the problem of correct exposure can not always be solved by 
reference to correct exposure technic for supersensitive panchromatic negative 
films. Actinometers, or exposure meters, are of little assistance under these dim 
light conditions since the camera position is usually remote from the subject, 
which, in turn, is often inaccessible for average brightness measurements. More- 
over, the photographic subjects made practicable by the Ultra-Speed panchro- 
matic film usually have too low a brightness level to activate photoelectric ex- 
posure meters in common use. Fortunately the sensitivity characteristics of the 
new film are sufficient to produce successful pictures under typical indoor illumina- 
tion, with normal shutter angles and at camera speeds of 24 frames a second, using 

* Received May 4, 1938. 
** Agfa Ansco Corp., Binghamton, N. Y. 


FIG. 1. Airplane view of New York City: Taken about 
7:30 P.M., Nov., 1937, on Ultra-Speed panchromatic negative 
film in Akeley silent camera with 2-inch //1. 4 lens, by News of the 

FIG. 2. Counting ballots in New York City Armory: Photographed 
by Pathe News on Ultra-Speed panchromatic film without additional 



lenses having relative apertures of f/2.3 and, in some cases, //3.5 (Fig. 2). The 
speed of the film is not appreciably affected by age. No allowances need be made 


Mochine developed in Agfa 17 


FIG. 3. Characteristic curves obtained by exposing 
Ultra-Speed panchromatic film in a Type 116 sensitom- 
eter and developing on a motion picture negative 
developing machine. 

in exposing old film since the Ultra-Speed film has proved to have exceptional 
stability with respect to speed and gradation, as well as resistance to fog and de- 
terioration during a period of eleven months. 


FIG. 4. Wedge spectrograms (tungsten) on Superpan negative and Ultra- 
Speed panchromatic film. 

In newsreel cameras that record sound on the same film with the picture image, 
a reduction of lamp current of approximately 15 per cent has been found adequate 



to compensate for the speed difference between Ultra-Speed panchromatic film 
and supersensitive panchromatic negative films. The introduction of a Wratten 
No. 47 (C-5 tricolor blue) filter into the optical system of the recorder accom- 
plishes the same purpose without requiring alteration of the lamp current. 

FIG. 5. Photographs of color charts by light of daylight quality on Superpan 
negative (left) and Ultra-Speed panchromatic film (right}. 

When exposed on typical sensitometers available in commercial motion picture 
laboratories, Ultra-Speed panchromatic film records density on all the steps 
(Fig. 3) because, when these instruments were designed, films having the sensi- 
tivity of Ultra-Speed panchromatic film possibly were not contemplated ; whence 



Anti Abrasion Surface 

Second Emulsion Layer 

,* Elision Lo,er 
Non Halation Cray Base Layer 

Nitrocellulose Film Base 

FIG. b. Structure of Agfa motion picture negative film, 
showing location of gray anti-halo layer. 

the sensitometers have been calibrated to suit the speed characteristics of the 
supersensitive panchromatic .emulsions. In order to study the threshold or 
shadow density characteristics of the Ultra-Speed film, the addition of a 25 per 
cent neutral density filter has been found advisable, since it produces sensito- 
metric strips having the required range of density without alt ering the character- 
istics of the lamp or disturbing the calibration of the sensitometer. 

Sept., 1938J 



Other Problems of Exposure. The speed advantage of two diaphragm stops, 
of Ultra-Speed panchromatic over Superpan negative film, is fairly constant under 
various daylight and artificial lighting conditions, 2 indicating close similarity in 
the color-sensitivity characteristics of the two films. Wedge spectrograms, how- 
ever, show that the Ultra-Speed film has a slightly greater range of sensitivity to 
red light than the previous film (Fig. 4) and photographs of the color chart (Fig. 
5) show that Ultra-Speed panchromatic film has about 20 per cent greater re- 
sponse to red-colored objects than the old Superpan negative film. The photo- 
graphic problem introduced by these color-sensitivity dissimilarities is not great and 
in most cases can be neglected with confidence. No special character make-up has 
been found necessary with the Ultra-Speed film even under 100 per cent tungsten 

Problems of Printing and Development. In timing negatives made on Ultra- 
Speed and Superpan negative film, no allowances need be made for differences 
in the gray-base color, since they both have the same type of neutral gray anti- 
halation layer (Fig. 6) on the base 
underneath the emulsion. When com- 
bined for printing with other negatives 
having lavender, pink, or orange-tinted 
gray bases of similar optical density, 
the Ultra-Speed panchromatic film 
may appear to be only three times 
instead of four times as fast, due to 
selective absorption of the printing 
light 2 by the tinted gray bases. From 
three to five printer points may be 
required to compensate for the filter 



16 2O 24 28 MINUTES 

FIG. 7. Gamma vs. developing 
time relationship of Ultra-Speed 
panchromatic Supreme, and Super- 
pan negative films. 

effect of tinted gray bases that depart 
markedly from a neutral gray. 

When developed for a gamma of 
0.65 or lower, Ultra-Speed panchro- 
matic film has a flatter gradation than 
Superpan negative film given the same treatment (Fig. 7). When developed 
for a gamma of 0.7 or higher, the Ultra-Speed film becomes progressively 
steeper in gradation than Superpan negative film given the same treatment. 
Considering the contrast relationship of the two films in the range of negative 
gamma normally employed in professional motion picture work, together with 
the photographic characteristics of the subjects that usually will be photo- 
graphed on Ultra-Speed panchromatic film, best screen results appear to follow 
the practice of developing Ultra-Speed panchromatic film about 20 per cent 
longer than Superpan negative film. 

In professional motion picture work, Ultra-Speed panchromatic film will, of 
necessity, be developed under normal negative processing conditions in prevailing 
types of developer, with the correction in time of development noted above. 
Tests with a number of developer solutions of interest to the photographer who 
uses motion picture negative film in miniature cameras for still photography have 
shown that Ultra-Speed panchromatic film behaves at least as well as Superpan 
negative in these solutions. For example, the rate of exhaustion of developer 















FIG. 8. Rate of exhaustion of developer by successive 
units of Ultra-Speed and Superpan negative films. The 
exhaustion rates of two different developers are also 

Sept., 1938] 



per unit of film developed was the same for Ultra-Speed panchromatic film as it 
was for Superpan negative (Fig. 8). Experience gained in processing typical 
motion picture negative films can be freely applied to the development of Ultra- 
Speed panchromatic film. 

No advantage is gained with the Ultra-Speed film by the use of fine-grain de- 
velopers of the sort that reduce the speed of the film. Greater efficiency and 


AT 6S'F. 





FIG. 9. Characteristic curves of Ultra-Speed panchromatic film developed 
in various solutions used for miniature camera photography on motion picture 
negative film. 

better photographic quality is assured by employing a film such as Supreme 
negative, 3 which is already slower than Ultra-Speed panchromatic film (but twice 
as fast as Superpan negative) and capable of exceptionally fine-grain results in 
motion picture negative developers of the types that bring out the full speed of 
the film. 

The sensitometric characteristics of Ultra-Speed panchromatic film developed 
in a number of developer solutions used with miniature camera exposures on 
motion picture negative film are shown in Fig. 9, and the time-gamma informa- 


tion obtained in these studies is compared in Table I. These data, in some 
cases, differ from recommendations already given for use with some of the solu- 
tions in developing Ultra-Speed panchromatic film. The effect of the several de- 
velopers upon the speed of the film parallels the results obtained with other nega- 
tive films : the highest effective film speeds were obtained with developers of the 
motion picture borax type, while the lowest speeds were obtained with the 


Gamma Obtained in Various Solutions by Tray Development of Ultra-Speed Pan- 
chromatic Film at 65 F 

Developing time in minutes 8 12 16 20 24 

Agfa 17 0.36 0.56 0.65 0.70 

SeaseNo. 3 0.33 0.50 

Infinol 0.40 0.52 0.62 0.67 0.82 

Finegrainol F-l^l 0.41 0.51 0.63 0.72 

M. P. G. 0.55 0.64 0.76 

Edwam 0.48 0.58 0.64 0.74 

Champlinl5 0.43 0.44 0.55 0.57 

paraphenylenediamine-glycin developers, and intermediate speeds resulted from 
the latter type of developer solution fortified by additions of metol. A com- 
parison of the relative speed attained with the Ultra-Speed film in the different 
developers is shown in Table II, the relationships being expressed in terms of 
stops and half-stops on the lens diaphragm that would produce similar negatives 
under the different conditions of development. 


Approximate Diaphragm Stop Required to Produce Negatives of Same Density 
on Ultra-Speed Film Using Different Developer Solutions 

Diaphragm Stop 

Agfa 17 //16 

Sease No. 3 11 

Infinol 16 

Finegrainol F-ll 16 

M. P. G. 8 

Edwal 12 11 

Champlin 15 12.5 

Safelight Requirements. So sensitive is Ultra-Speed panchromatic film to light 
of all colors that it must be handled and developed in total darkness. Green 
safelight filters that have proved practicable for use with supersensitive panchro- 
matic film will fog the Ultra-Speed film. Very brief inspection of the wet film is 
permissible during development, using a panchromatic green safelight such as the 
Agfa No. 108 with one-half the illumination that would be safe for supersensitive 
panchromatic film. 



1 HuSE, E., AND CHAMBERS, G. A.: "Eastman Supersensitive Motion Picture 
Negative Film," /. Soc. Mot. Pic. Eng., XVII (Oct., 1931), No. 4, p. 560. 

HUSE, E., AND CHAMBERS, G. A.: "Eastman Super X Panchromatic Nega- 
tive Motion Picture Film," Amer. Cinemat. XVI (May, 1935), No. 5, p. 186. 

2 ARNOLD, P. H.: "Sensitivity Tests with an Ultra-Speed Negative Film," 
/. Soc. Mot. Pict. Eng., XX (May, 1938), No. 5, p. 541. 

3 STULL, W.: Amer. Cinemat., XIX (Jan., 1938), No. 1, p. 10. 



The light-valve described in this paper has been designed specifically as a part 
of recently developed portable recording equipment when used for push-pull 
recording. As space is limited in portable equipment, the light-valve was de- 
signed to obtain the smallest practical mechanical structure and yet allow the 
adjustment and maintenance advantages of the standard four-ribbon valve used 
with fixed channel recording machines. 




FIG. 1. Showing arrangement of pole-pieces and base 

Referring to Fig. 1, it will be noted that four of the pole-pieces (there are four 
on the bottom and four on the top) are mounted in a shallow slot in a soft steel 
base-plate. The pole-pieces are accurately machined pieces of "Permendur," 

* Presented at the Spring, 1938, Meeting at Washington, D. C. ; received 
April 20, 1938. 

** Electrical Research Products, Inc., Hollywood, Calif. 



a material having the characteristic of high flux transmitting capacity. The 
pole-pieces are located in the proper position on the base-plate, as well as the cap- 
plate, by means of an assembly jig and are locked in place by small screws. Pass- 

FIG. 2. Top view of pole-piece assembly. 

ing through the sides of the pole-pieces on the base-plate are holes so located in 
each piece as to form a continuous through hole for each pair of poles when prop- 
erly assembled on the base-plate. This hole is a clearance hole for a through 
screw that holds the ribbon clamping and adjusting bar assembly to the sides of 
the pole-piece structure. The arrangement is shown in Fig. 2. The clamping 





FIG. 3. Clamping bar. 

bars, one of which is shown in Fig. 3, are made of steel hardened after machining. 
The overall length L of all eight bars is identical, but the height H and the dis- 
tance D vary. The variation in height H is to allow the ribbons, when clamped, 
to lie in different planes so that they can pass without clashing. In addition, the 
two end bars on each side are provided with means to move the clamping edge 

Sept., 1938] 



along the ribbon line for ribbon-tension adjustment. The ribbon-clamping caps 
are made of steel and are the same for all the clamping bars. 

The holes for the screws holding the clamping bars against the sides of the 



FIG. 4. Cross-sectional view showing positioning of ribbons. 

pole-pieces are of sufficient size to allow electrical insulation between the clamp 
bars and the clamping screws. The individual clamping bars are insulated from 
each other by means of thin bakelite washers 0.012 inch thick. The electrical 
connections are made at either end of the clamping bars by means of a stiff con- 

FIG. 5. Arrangement of ribbons over pole-pieces. 

necting wire set in a small hole and locked in place by a set screw. To locate the 
clamping bars properly on each side of the pole-piece structure, a jig is used during 
assembly which aids in obtaining the proper height H and the proper distance D 
of all the bars 



The cross-section position of the ribbons when placed between the clamping 
points is shown schematically in Fig. 4. It will be noted that ribbons A and C 
are placed on a horizontal plane 0.002 inch above the top faces of the pole-pieces, 
whereas B and D are placed slightly higher to give about 0.0015 inch of clearance 
between the two sets of ribbons. Ribbons A and B act as one pair and C and D 
as the other pair, but being offset in height, they will not mechanically clash if the 

6. Refractor prisms. 

ribbon amplitude should momentarily exceed the prescribed amount. The 
spacing for either pair of ribbons can be set for rather wide limits, but normally 
it is 0.001 inch. The center-lines of the two pairs of ribbons are spaced 0.016 
inch apart. 

Fig. 5 schematically shows how the individual ribbons are arranged over the 
pole-pieces. It shows how the two end-clamps are arranged to allow tuning ad- 
justment for any ribbon, as well as how the electrical connections are made. It 

FIG 7. Light-valve and double-magnet assembly. 

will be noted that although all the ribbons are of the same length, the dimensions 
are such that the longitudinal center of each ribbon coincides very closely with 
the center of its associated pole-piece opening, thereby minimizing bowing effect. 
Inasmuch as the center-lines of the two ribbon pairs are located 0.016 of an 
inch apart, means must be provided to align these center-lines at the film. This 
is done by small refractor plates mounted in the cap pole-pieces, the principle of 
which is shown schematically in Fig. 6. One refractor plate and one pair of rib- 
bons are shown solid in this sketch, whereas the other set is shown dotted. The 


rays from the condenser lens pass through the light-valve ribbon opening and 
strike the glass refractor plates at an angle. The rays are then refracted 
toward the normal, depending upon the angle of the plate and its index of refrac- 
tion, and emerge from the other side of the refractor plate at the same angle at 
which they entered, but displaced in the vertical plane, provided the sides of the 
refractor plates are optically parallel to each other. Thus the objective lens sees 
the two halves of the light- valve ribbon openings as if they were in line. 

The magnetic flux for the ribbon air-gap is supplied by two permanent magnets 
made of "Alnico." This material is an alloy of iron, aluminum, cobalt, and nickel, 
and has the characteristic of very high retentivity along with high magnetomotive 
force, the latter determining the value of light-valve sensitivity. 

Stringing and adjusting the ribbons of this new type of light-valve is reasonably 
simple. As already mentioned, separate screw adjustments are provided for 
spacing and tuning each ribbon independently, even after the light-valve is com- 
pletely assembled. 

The entire light-valve and double-magnet assembly is quite compact, as shown 
in Fig. 7. The overall dimensions of the unit are 1.4 inch wide, 1 inch thick, and 
4 inches long overall. The overload point is about 9 db. above 0.006 watt, and 
the closure current approximately 170 milliamperes per ribbon. Field tests under 
actual operating conditions have shown this type of valve to be very constant in 
performance and easy to maintain in proper adjustment. 


H. A. DsYRY** 

The motion picture projection machine has undergone fewer radical changes 
and improvements than perhaps any other mechanical electrical device in daily 
use by so many thousands. This is due partly to the fact that the old designers 
did a very good job so that radical improvements seemed improbable. However, 
any mechanical contrivance or machine that has suffered no changes except re- 
finements in 15 to 20 years can hardly be expected to be a really modern machine. 

With this thought in mind we have developed not only an improvement, at least 
so far as simplicity and cost are concerned, but quite a novel and unique applica- 
tion of a silent chain drive, which so far as we or the manufacturer of the chain 
know, has not been made before. 

The feature of the device lies in changing the course of the chain without affect- 
ing the shutter. Both shutter and sprocket are motivated by the same chain 
(Fig. 1). 

* Presented at the Spring, 1938, Meeting at Washington, D, C.; received 
February 25, 1938. 
** H. A. DeVry Corp,, Chicago, III 


Our original idea of about three years ago was to frame the intermittent sprocket 
straight up and down below the aperture, which worked out very satisfactorily in 
hundreds of machines in all parts of the world. Another advantage of the first 
model was that by removing three screws the entire intermittent assembly can be 
exchanged or replaced practically between reels. 







FIG. 1. Framer in neutral position; moving lever to the right 
moves film up, and vice versa. 

The only disadvantage of this framing method, if it can be called a disadvantage, 
was that when the intermittent sprocket was positioned all the way down (which, 
of course, is not necessary when threaded by a good projectionist), it left a space 
of the height of one frame between the aperture plate and the sprocket, which 
might cause some film to buckle slightly at that point by slightly overthrowing the 

When this was called to our attention this objection was overcome by a slightly 
different application of the same basic principle. The revolving intermittent 
sprocket framer was arranged as in Fig. 2. Note that at the point indicated by 
the arrow, there is no possibility of film buckling, as the sprocket always remains 
close to the gate, regardless of the position of the film. 

Sept., 1938] 



This particular type of chain drive thus achieves freedom from film buckling 
while framing, and also removes the possibility of the shutter's being put out of 
synchronism with the film. In addition, the cost of manufacture is cut to the 

FIG. 2. 

Showing arrangement of intermittent sprocket 

The advantage of the silent chain drive is perhaps best attested by the fact 
that the Ford Motor Company, like Cadillac, Chrysler, and other automobile 
manufacturers, use silent chains for driving cam shafts, which is perhaps the 
most particular job on an automobile engine. 



The editors present for convenient reference a list of articles dealing with subjects 
cognate to motion picture engineering published in a number of selected journals. 
Photostatic copies may be obtained from the Library of Congress, Washington, D. C., 
or from the New York Public Library, New York, N. Y. Micro copies of articles 
in those magazines that are available may be obtained from the Bibliofilm Service, 
Department of Agriculture, Washington, D. C. 


18 (June, 1938), No. 6 

Video Amplifier Design (pp. 13, 30). A. W. BARBER 

Features of 1939 Receivers (pp. 15-18). D. D. COLE, G. G. 



11 (June, 1938), No. 6 
Television I-F Amplifiers (pp. 20-23). E. W. ENGSTROM AND 


Rectifier Filter Design (pp. 28-30). H. J. SCOTT 

A Sound Effects Machine with High Impedance Mixing M. J. WEINER 
(pp. 56, 58). 

International Photographer 

10 (June, 1938), No. 5 
Developing Machines (p. 8). 

Optical Printer Handy Andy (pp. 14, 16). L. DUNN 

Slyfield's New Mixers' Gallows (p. 18). J. N. A. HAWKINS 


20 (June, 1938), No. 6 
Flimmern und Bildwandbeleuchtung (Flicker and 

Screen Illumination) (pp. 141-143). H. NAUMANN 

Der Farbenausgleich zwischen Szenen und Szenen- 
teilen beim Farbenfilm (Color Balancing between 
Scenes and Parts of .Scenes in Color-Films) (pp. 
143-144). L. KUTZLEB 

Uber die Berechnung photographischer Belichtungen 
(Computation of Photographic Exposure) (pp. 145- 
148). G. ALBRECHT 


>t., 1938] CURRENT LITERATURE 323 

Quecksilberdampflampen hoher Leuchtdichte (High- O. HOPCKE AND 
Intensity Mercury Vapor Lamps) (pp. 148-152). W. THOURET 

Ein neuer Projektor fur 8-Mm.-Film (New 8-Mm. Pro- 
jector (Dralowid)) (p. 153). 

Photographische Industrie 

36 (June 15, 1938), No. 24 

Die Bedeutung des elektrischen Belichtungsmessers fiir 
die Kinematographie I (Importance of Electrical 
Exposure Meters for Motion Picture Photography I) 
(pp. 705-707). H. C. OPFERMANN 

Technique Cinematographique 

9 (May, 1938), No. 89 

Nouvel objectif pour le radiocinematographe (New 
Lens for X-ray Cinematography) (pp. 1171-1172). 


11 (June, 1938), No. 124 

Baird Still-Picture Transmitter (pp. 324, 341). 

The London Television Service (pp. 329-331). T. C. MACNAMARA AND 

Mihaly-Traub Television (p. 336). 
The Receiving Aerial and Reception Fidelity (pp. 
342-343). S. W. SEELEY 


Motion Picture Sound Engineering: A symposium of papers on Studio Sound 
Recording and Theater Sound Reproducing Equipment and Practice, Academy 
of Motion Picture Arts & Sciences (Taft Building, Hollywood, Calif.), $4.00. 

This book results from courses in motion picture sound engineering conducted 
during 1936 and 1937 by the Research Council of the Academy of Motion Picture 
Arts & Sciences, the lecturers being the qualified representatives of the major 
sound departments. There are thirty-nine chapters, of which the first ten relate 
to the practice of sound recording in studios and sound reproducing in theaters, 
while the succeeding chapters are concerned with transmission circuits and elec- 
tromagnetic theory. 

After an excellent introductory chapter on the basis of motion picture sound, 
the text proceeds to discuss the nature of sound, the types of film recording in use, 
the acoustic instruments used for sound pick-up and for monitoring, the mechani- 
cal and optical features of film propulsion and scanning, and the circumstances 
of theater sound reproduction. There are chapters explaining film processing and 
the artifices of noise-reduction as well as the more recent methods of recording, 
such as push-pull, squeeze-track, and pre- and post-equalization. In the discus- 
sion of these new methods there is much that, while not yet classical, dis- 
closes the processes of advance in sound picture engineering. 

While the text describes most of the steps currently employed in film recording 
and processing, there are a few omissions as, for example, in the chapter on film 
processing there is no reference to the useful delta-db. test in variable-density 
work or of the intermodulation tests regularly used to determine the optimal 
processing of variable-width sound-track. 

Although the book is devoted to photographic methods, there might well be 
a place for a short discussion of disk recording and reproduction, which has a 
definite place for play -back and pre-scoring. The references to loud speakers 
likewise might well be amplified to include descriptions of the various types of re- 
ceivers, horns, and baffles in commercial use. 

The earlier chapters, / to X, are descriptive of apparatus and processes of in- 
terest to the general reader, telling him what the sound engineer has to do and 
how he does it. The subsequent chapters are for the electrical engineer, with 
particular reference to the mathematical problems of the sound engineer. They 
apply to the design rather than the operation of sound equipment. 

The Academy of Motion Picture Arts & Sciences is to be congratulated upon 
having sponsored the training courses that resulted in the publication of such 
a useful compilation of information dealing with the relatively new science of 
sound recording and reproduction. 









Officers and Committees in Charge 

W. C. KUNZMANN, Convention Vice-President 
J. I. CRABTREE, Editorial Vice-President 
G. E. MATTHEWS, Chairman, Papers Committee 
H. GRIFFIN, Chairman, Projection Committee 
E. R. GEIB, Chairman, Membership Committee 
J. HABER, Chairman, Publicity Committee 

Local Arrangements 

K. BRENKERT, Chairman 




Registration and Information 

W. C. KUNZMANN, Chairman 



Hotel and Transportation Committee 

A. J. BRADFORD, Chairman 






H. GRIFFIN, Chairman 






Officers and Members of Detroit Projectionists Local No. 199 



J. F. STRICKLER, Chairman 



326 FALL CONVENTION [j. s. M. p. E. 


J. HABER, Chairman 



Ladies 1 Reception Committee 

MRS. J. F. STRICKLER, Hostess 

assisted by 





The Headquarters of the Convention will be at the Hotel Statler, where excellent 
accommodations are assured. A reception suite will be provided for the Ladies' 
Committee, who are now engaged in preparing an excellent program of entertain- 
ment for the ladies attending the Convention. 

Special hotel rates guaranteed to SMPE delegates and friends, European plan, 
will be as follows : 

One person, room and bath $3.00 to $6.00 

Two persons, room and bath 5.00 to 8.00 

Two persons (twin beds), room and bath 5.50 to 9.00 

Three persons, room and bath 7.50 to 10.50 

Parlor suite and bath, for one 8.50 to 11.00 

Parlor suite and bath, for two 12.00 to 14.00 

Room reservation cards will be mailed to the membership of the Society in the 
near future, and everyone who plans to attend the Convention should return his 
card to the Hotel promptly in order to be assured of satisfactory accommodations. 
Registrations will be made in the order in which the cards are received. Local 
railroad ticket agents should be consulted as regards train schedules, and rates to 
Detroit and return. 

The following special rates have been arranged for SMPE delegates who motor 
to the Convention, at the National-Detroit Fireproof Garage (the Hotel Statler's 
official garage), Clifford and Elizabeth Streets, Detroit: Self -delivery and pick-up, 
12 hours, $0.60; 24 hours, $1.00; Hotel-delivery and pick-up, 24 hours, $1.25. 
Special weekly rates will be available. 

Technical Sessions 

An attractive and interesting program of technical papers and presentations is 
being assembled by the Papers Committee. All technical sessions, apparatus 
symposiums, and film programs will be held in the Large Banquet Room of the 

Registration and Information 

Registration headquarters will be located at the entrance of the Large Banquet 
Room, where members of the Society and guests are expected to register and re- 
ceive their badges and identification cards for admittance to the sessions and film 

Sept., 1938] FALL CONVENTION 327 

programs. These cards will be honored also at the Fox Detroit Theater, through 
the courtesy of Mr. David Idzol, and special passes will be furnished to registered 
members and guests for admittance to the Michigan United Artists and Palms- 
State Theaters, through the courtesy of the United Detroit Theaters Corporation. 

Informal Luncheon and Semi- Annual Banquet 

The usual Informal Luncheon will be held at noon of the opening day of the 
Convention, October 31st, in the Michigan Room of the Hotel. On the evening of 
Wednesday, November 2nd, the Semi- Annual Banquet of the Society will be held 
in the Grand Ballroom of the Hotel at 8 P.M. Addresses will be delivered by 
prominent members of the industry, followed by dancing and other entertainment. 

Tours and Points of Interest 

In view of the fact that this Convention will be limited to three days, no 
recreational program or tours have been arranged. However, arrangements 
may be made for visits to the Jam Handy plant and to other points of technical 
and general interest in Detroit on the day following the Convention, namely, 
November 3rd. Arrangements for such trips may be made at the registration 
headquarters of the Convention. 

In addition to being a great industrial center, Detroit is also well known for the 
beauty of its parkways and buildings, and its many artistic and cultural activities. 
Among the important buildings that one may well visit are the Detroit Institute 
of Arts; the Detroit Historical Society Museum; the Russell A. Alger House, a 
branch of the Detroit Institute of Arts; the Cranbrook Institutions; the Shrine 
of the Little Flower; and the Penobscot Building. 

At Greenfield Village, Dearborn, are grouped hundreds of interesting relics of 
early American life, and there also is located the Edison Institute, established by 
Henry Ford in memory of Thomas A. Edison. 

On the way to Greenfield Village is the Ford Rotunda, a reception hall for visi- 
tors to the Ford Rouge Plant. Here' are complete reproductions and displays of 
motorcar design, and representations of the famous highways of the world, from 
Roman days to modern, are on the grounds surrounding the building. 

The General Motors Research Building and Laboratory, located on Milwaukee 
Avenue, will be of particular interest to engineers visiting the City. 

Various trips may be taken from Detroit as a center to Canada, by either the 
Ambassador Bridge or the Fleetway Tunnel; to Bloomfield Hills, a region of 
lakes; Canadian Lake Erie trip from Windsor, Ontario; to Flint, Michigan, 
another center of the automotive industry; to Milford, General Motors' Proving 
Grounds; and to the Thumb of Michigan Resort Beaches. The City contains 
also a number of beautiful parks and golf courses. 

S. M. P. E. 


These films have been prepared under the supervision of the Projection 
Practice Committee of the Society of Motion Picture Engineers, and are 
designed to be used in theaters, review rooms, exchanges, laboratories, 
factories, and the like for testing the performance of projectors. 

Only complete reels, as described below, are available (no short sections 
or single frequencies). The prices given include shipping charges to all 
points within the United States ; shipping charges to other countries are 

35-Mm. Sound-Film 

Approximately 500 feet long, consisting of recordings of several speak- 
ing voices, piano, and orchestra; buzz-track; fixed frequencies for focus- 
ing sound optical system; fixed frequencies at constant level, for de- 
termining reproducer characteristics, frequency range, flutter, sound- 
track adjustment, 60- or 96-cycle modulation, etc. 

The recorded frequency range of the voice and music extends to 10,000 
cps. ; the constant-amplitude frequencies are in 15 steps from 50 cps. to 
10,000 cps. 

Price $37.50 each, including instructions. 

35-Mm. Visual Film 

Approximately 500 feet long, consisting of special targets with the aid 
of which travel-ghost, marginal and radial lens aberrations, definition, 
picture jump, and film weave may be detected and corrected. 

Price $37.50 each, including instructions. 

16-Mm. Sound-Film 

Approximately 400 feet long; contents identical to those of the 35-mm. 
sound-film, with the exception that the recorded frequency range ex- 
tends to 6000 cps., and the constant-amplitude frequencies are in 11 
steps from 50 cps. to 6000 cps. 

Price $25.00 each, including instructions. 

16-Mm. Visual Film 

An optical reduction of the 35-mm. visual test-film, identical as to 
contents and approximately 400 feet long. 
Price $25.00 each, including instructions. 







Volume XXXI OCTOBER, 1938 Number 4 



The Theory of Three-Color Photography A. C. HARDY 331 

The Fundamentals of Color Measurement. . . . D. L. MACADAM 343 

Sound Pictures in Auditory Perspective F. L. HUNT 351 

Application of Electrical Networks to Sound Recording and 

Reproducing H. R. KIMBALL 358 

Multiple-Channel Recording. H. G. TASKER 381 

Some Unusual Adaptations of 16-Mm. Equipment for Special 

Purposes J. L. BOON 386 

An Improved Roller Type Developing Rack with Stationary 

Drive C. E. IVES 393 

New Apparatus 

A Continuous Optical Redaction Sound Printer 

M. G. TOWNSLEY and J. G. ZUBER 405 

A New 16-Mm. Projector H. C. WELLMAN 410 

A Novel Surgical Filming Stand .A. LENARD 413 

Current Motion Picture Literature 418 

Fall Convention at Detroit 

General 421 

Abstracts of Papers 424 

Society Announcements 435 

Obituary Norman McClintock 438 





Board of Editors 
J. I. CRABTREE, Chairman 



Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, 
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West-Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
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"President: S. K. WOLF, 1270 Sixth Ave., New York, N. Y. 

* Past-President: H. G. TASKER, 5451 Marathon St., Hollywood, Calif. 
*Executive Vice-President: K. F. MORGAN, 6601 Romaine St., Los Angeles, 


** Engineering Vice-President: L. A. JONES, Kodak Park, Rochester, N. Y. 
"Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 
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* Convention Vice-President: W. C. KUNZMANN, Box 6087, Cleveland, Ohio. 
"Secretary: J. FRANK, JR., 90 Gold St., New York, N. Y. 

"Treasurer: L. W. DAVEE, 76 Varick St., New York, N. Y. 


*J. O. AALBERG, 6920 McKinley St., Los Angeles, Calif. 
*M. C. BATSEL, Front and Market Sts., Camden, N. J. 
**R. E. FARNHAM, Nela Park, Cleveland, Ohio. 
*G. FRIEDL, JR., 90 Gold St.; New York, N. Y. 
*A. N. GOLDSMITH, 444 Madison Ave., New York, N. Y. 
**H. GRIFFIN, 90 Gold St., New York, N. Y. 

**A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 
*S. A. LUKES, 6427 Sheridan Rd., Chicago, 111. 
*Term expires December 31, 1938. 
**Term expires December 31. 1939. 

A. C. HARDY** 

Summary. All methods of three-color photography are the outgrowth of a sugges- 
tion made in 1855 by Clerk Maxwell, the illustrious British physicist. The method 
that he suggested would now be classed as an additive process, since the final reproduc- 
tion was effected by projecting three lantern-slides in register on the same screen; 
one lantern being supplied with a red filter, one with a green filter* and one with a blue 
filter. Maxwell suggested further that these lantern- slides be prepared from three 
negatives, each negative being exposed through the same filter that was to be used 
in projecting the corresponding lantern-slide. An extension of Maxwell's reason- 
ing to subtractive processes leads to the conclusion that the dyes used in the pro- 
duction of the positive images should each be complementary in color to the corre- 
sponding taking filter. 

Despite Maxwell's intimation that his process was theoretically incapable of 
perfect reproduction, the basic features of Maxwell's reasoning have been incor- 
porated into the commonly accepted theory of color reproduction. The recent progress 
in the science of colorimetry has made it possible to investigate the relation that should 
obtain between the characteristics of the taking filters and the colors of the reproduction 
primaries. Such an investigation shows that the taking filters required for perfect 
reproduction have characteristics that are very different from those in common use. 

The paper is concerned with the establishment of the conditions that lead to faithful 
reproduction by any three-color process. Examples of the application of these funda- 
mental conditions are given for both additive and subtractive processes. 

In another paper 1 presented at the Washington Convention of the 
Society, D. L. MacAdam showed that colorimetry has now acquired 
the status of an exact science. The motion picture film that he 
exhibited demonstrated how this science can be employed to test 
the faithfulness of any process of color photography. In this appli- 
cation, colorimetry plays a role not unlike that of the calipers in the 
hands of a machinist who undertakes to duplicate a.mechanical part 
in a machine shop. By means of the calipers, the machinist is able 
to compare the dimensions of the reproduction with the corresponding 
dimensions of the original. 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
June 22, 1938. 

** Massachusetts Institute of Technology, Cambridge, Mass. 


332 A. C. HARDY [j. s. M. P. E. 

The purpose of this paper is to indicate the application of the sci- 
ence of colorimetry to the theory of color photography. This may be 
likened to the design of machinery that will produce automatically 
the result that the machinist achieves by trial and error. More 
specifically, this paper is concerned with the determination of the 
characteristics of three color niters which, when used as taking filters 
in a three-color process, will enable negatives to be made that will 
control the reproduction primaries properly at every point of the re- 

Let the subject contain an area whose color can be characterized 
by the statement that the light received from this area by the camera 
lens has a spectral distribution of energy E. The tristimulus values 
of this area are 1 

X = I Exd\, (la) 

Y = \ Eyd\, (ib) 



Z = Ezd\, (Ic) 


where x, y, and z are the tristimulus values of unit amounts of the 
spectrum colors in the colorimetric system employed. 

Suppose the tristimulus values of unit amounts of the primaries 
that are mixed to form the positive reproduction are X T YfZ rJ X g Y g Z g> 
and X b Y b Z b , respectively. Then, if an area of the reproduction con- 
tains r units of the red primary, g of the green, and b of the blue, the 
tristimulus values of this area are 

X' = rX r + gX g + bX b , (2a) 

Y' = rY r + gY a + bY b , (2b) 

Z' = rZ r + gZ a + bZ b . (2c) 

If this area of the reproduction is to evoke the same visual sensa- 
tion as the area of the subject characterized by the energy distribu- 
tion E, the necessary condition is 

X' = X, (3a) 

Y' = Y, (3b) 

Z' = Z. (3c) 

Over a wide range of brightness level, the reproduction would be en- 
tirely satisfactory if the tristimulus values of the reproduction are 


proportional, but not necessarily equal, to those of the corresponding 
area of the original. 

The first step in virtually all methods of three-color reproduction is 
the making of three color-separation negatives (or the equivalent). 
To simplify the mathematical expressions, let the effective spectral 
sensitivity of the three negative emulsions be represented by S r , S g , 
and S b , respectively, it being understood that the effective sensitivity 
at each wavelength is the product of the inherent sensitivity of the 
emulsion and the transmittance of the filter used in conjunction 
therewith. When these three emulsions are exposed to the area of 
the subject characterized by a spectral distribution of energy E, the 
three exposures are proportional, respectively, to 

r = f 





ES b d\. (4c) 

When one follows the conventional procedures, each exposure de- 
termines the amount of one of the reproduction primaries. If the 
conditions for tone reproduction are satisfied, 

r = k,? r , (5a) 

g = k ? B> (5b) 

b = k b ? b . (5c) 

These five sets of equations may be combined algebraically to yield 
the following equations : 

k r X r f ES r d\ + k X g f ES g d\ + k b X b \ ES b d\ = ] Exd\, (6a) 

Jo Jo Jo Jo 

k T Y r ] ES r d\ + k g Y g f ESgd\ + k b Y b f ESbd\ = ( Eyd\, (6b) 

Jo Jo Jo Jo 

k r Z r f ES r d\ + k g Z g f ESgdX + k b Z b \ ES b d\ = \ Ezd\, (6c) 

Jo Jo Jo Jo 

which define the necessary and sufficient conditions that one color in 
the subject be reproduced correctly. Inspection of these equations 
reveals that one color in the subject may be reproduced correctly in 
an infinite number of ways. In other words, regardless of the form 
of the functions S T , S g , and S b or the tristimulus values of the repro- 

334 A. C. HARDY [j. s. M. P. E. 

duction primaries, the constants may always be chosen in such a 
manner that equations 6 will be satisfied for one color of the subject. 
The usual desideratum in color photography is to reproduce cor- 
rectly all colors of the subject that lie within the realizable color 
gamut. This means in mathematical language that equations 6 
must be satisfied simultaneously, regardless of the form of the func- 
tion E. This will be true if at every wavelength 

k r X r S r + k a X S a + k b X b S b = X, (7a) 

krY r S r + k g Y S g + k b Y b S b = J, (7b) 

k r Z T S r + k g Z 6 S + k b Z b S b = I. (7c) 

Since only relative values of S r , S g , and S b are required in practice, 
equations 7 can be written more simply in terms of the trichromatic 
coefiicients of the reproduction primaries rather than in terms of 
their tristimulus values. When this is done, the fundamental condi- 
tions for exact color reproduction by a three-color process become 

x r S r + x g S g + x b S b = x, (8a) 

yrS r + y S g + y b S b = y, (8b) 

Z r S r + Z g S g + Z b S b = Z. (8 C ) 

To avoid misunderstanding, it may be added that these conditions 
are perfectly general in the sense that the colors of the subject may be 
either real or imaginary. Likewise, the reproduction primaries may 
be either real or imaginary. In a practical process, the reproduction 
primaries are real, and negative amounts of the primaries can not be 
employed. This limits the realizable color gamut, but it in no way 
alters the fundamental requirements which must be fulfilled by any 
three-color process, real or imaginary. 

The application of equations 8 to additive processes is immediately 
evident. In such processes, the trichromatic coefficients of the pri- 
maries are easily ascertained by the application of procedures that 
are well standardized in the field of colorimetry. Likewise, the tri- 
stimulus values of unit amounts of the spectrum colors are well known 
for a normal observer. 2 Equations 8 can thus be solved for the values 
S r> S g , and S b at each wavelength. Then, knowing the spectral sen- 
sitivities of the emulsions to be employed, the characteristics of the 
required color filters can be computed. 

The application of these equations to subtractive processes is not 
so obvious, largely because of the uncertainty concerning the values 
that should be used for the trichromatic coefficients of the primaries. 


In an ideal subtractive process, each dye absorbs light uniformly in a 
spectral region that is not absorbed by the other two. Thus, each 
reproduction primary is determined by the color of the light absorbed 
by one of the three dyes. In this ideal case, it is a simple matter to 
determine the trichromatic coefficients of the primaries. By sub- 
stituting their values in equations 8, the required spectral sensitivities 
of the color-separation negatives can readily be determined. 

With the dyes that are available for use in subtractive processes, it 
is impossible to assume that, at every wavelength, the absorption of 
light is produced by the action of one dye alone. Instead, the pri- 
maries of subtractive processes must be determined under conditions 
that take account of the actual behavior of the dyes. A method by 
which this can be accomplished will be clear from the spectrophoto- 
metric curves shown in Fig. 1. It will be noted that curve F is the 
same in all three illustrations. This curve represents the spectral 
transmittance curve of a piece of color-film whose color is such that 
it would produce a light flesh tint when projected upon the screen. 
A flesh tint was chosen as the color of reference partly because of its 
importance in color photography and partly because it is not far 
removed from the center of the realizable color solid. 

Now let another piece of film be prepared under identical conditions 
except that the concentration of the red-absorbing (blue-green) dye 
is slightly reduced. The spectral transmittance curve of this film is 
represented by curve R. It will be seen that reducing the concentra- 
tion of the red-absorbing dye has brought about an increase in the 
amount of red light transmitted by the film, as would be expected. 
More exactly, curve R', which is obtained by subtracting the ordi- 
nates of curve F from those of curve R, indicates the spectral dis- 
tribution of the light controlled by the red-absorbing dye, assuming 
the projection source to emit equal amounts of energy throughout 
the spectrum. The trichromatic coefficients computed from this 
curve, after modification by the energy distribution of the source, are 
the required values of x r , y r , and z r . By repeating the experiment of 
varying the concentration of one dye at a time, it is possible to find 
the trichromatic coefficients corresponding to curves G' and B' '. 
This procedure evidently determines the trichromatic coefficients of 
the primaries, which are needed for substitution in equations 8. 

When such a test is performed with the dyes that are now available, 
the trichromatic coefficients of the primaries are found to depend to 
some extent upon the color selected as the color of reference. Since 



[J. S. M. P. E. 











FIG. 1. These spectrophotometric curves illus- 
trate a method by which the reproduction pri- 
maries in a subtractive process can be identified. 







500 600 700 




SOO 600 




400 500 600 TOO 


FIG. 2. These curves indicate the relative 
spectral sensitivity of the three emulsions to 
be used in making three-color separation nega- 
tives that will control properly the reproduction 
primaries identified in Fig. 1. 

338 A. C. HARDY [j. s. M. P. E. 

a change in the trichromatic coefficients of the primaries should 
theoretically be compensated by a modification in the characteristics 
of the taking filters, the most useful expedient in practice is to deter- 
mine the trichromatic coefficients of the primaries for a color of ref- 
erence near the center of the realizable color solid. The various con- 
stants of the system may then be chosen in such a manner as ar- 
bitrarily to make the rendition correct for certain colors which should 
preferably lie near the outside of the realizable color solid. In this 
way, the errors in the color rendition are reduced everywhere to ap- 
proximately their minimum values. 

If one assumes a projection source having, for example, an energy 
distribution corresponding to that of the I.C.I. Illuminant C, the tri- 
chromatic coefficients calculated from curves R f , G', and B' of Fig. 1 
are as shown in Table I. 

Red Primary Green Primary Blue Primary 

x r = 0.4969 x g = 0.1985 * 6 = 0.1847 

y r = 0.3346 ^ = 0.4423 y b = 0.1265 

z r = 0.1685 z g = 0.3592 z b = 0.6889 

When these values are substituted in equations 8, the values of S r , 
S g , and S b are found to be as shown in Fig. 2. It will be recalled that 
the ordinates of these curves represent the effective spectral sensi- 
tivity (on a relative scale) of the three photographic emulsions that 
will result in the color-separation negatives that will properly con- 
trol the reproduction primaries identified by the method illustrated 
in Fig. 1. It will be noted that the required spectral sensitivity is less 
than zero at certain wavelengths, an effect that can not be achieved 
directly by means of color filters. In another publication, 3 numerous 
suggestions for the practical realization of the required negative 
values of the spectral sensitivity have been made. One method 
comprises making two negatives, the spectral sensitivity of each 
being such that, when the exposure of one is photographically 
subtracted from the exposure impressed upon the other, the result 
will simulate one of the curves in Fig. 2. Hence, by making a total 
of six negatives, the three primaries can be controlled properly. 

Although the above expedient is useful as an illustration of the 
application of the rigorous theory, a camera designed to expose six 
negatives simultaneously would be quite impracticable. Three nega- 
tives may be made to suffice, however, by abandoning the assumption 


incorporated in equations 5. Instead, let it be assumed that the 
amount of the red primary is to be made dependent to some extent 
upon the exposure received by all three color-separation negatives. 
If a similar assumption is made with respect to the green and blue 
primaries, equations 9 are an expression of the proposed technic. 

r = k&r + k& + k^ b , (9a) 

g = k*2 r + k g + k 6 2 bt (9b) 

b = k&r + ksZ g + k^ b . (9C) 

The practical realization of the technic indicated by these equations 
involves controlling the red primary, for example, by means of a 
photographic image of the subject that is a composite record of the 
exposure of the red negative, the exposure of the green negative, and 
the exposure of the blue negative. The extent to which each exposure 
is weighted by this record is determined by tr;e magnitude of the con- 
stants ki t kz, and & 3 . When one of the constants is less than zero, a 
positive image rather than a negative image is to be employed in 
making the composite record. Care must also be taken that the 
characteristics of the photographic materials are substantially linear, 
as in the toe method of sound recording, in order that a true addition 
or subtraction of exposures may be effected. 

With this understanding of the proposed technic, let equations 9 
be substituted in the previous development instead of equations 5. 
The conditions for correct color rendering are then found to take the 


KiSi + -K 2 S 2 + K 3 S 3 = x, (lOa) 

KiSt + K 5 S 2 + KeS 3 = y, (lOb) 

KjSi + K 8 S 2 + K g S 3 = z, (lOc) 

where the constants in the above equations (indicated by capital 
letters) have the following values : 

Ki = ktXr + k.X g + k 7 X b , 

Z = ksX r -f- k^Xg + kgX b , 

* = k,Y r + k,Y g + 
, = k 2 Y r + k,Y + 

* = k,Y r + k*Y g + 

-, = kiZ r + k*Z g + k 7 Z b , 

= k 2 Z r + k^ g + 

k 9 Z b . 

340 A. C. HARDY [j. s. M. P. E 

Equations 10 are of the same form as equations 7, and can be used in 
the same manner. In this case, the spectral sensitivities, S T , S g , and 
S b , may be everywhere positive and are therefore readily realizable in 
practice. Those familiar with the concepts of colorimetry will rec- 
ognize that this technic involves, in effect, the preparation of a set of 
three negatives which would properly control a set of imaginary re- 
production primaries. By making the additive and subtractive com- 
binations indicated by equations 9, a new set of negatives can be pre- 
pared that will properly control the reproduction primaries employed 
in any process, additive or subtractive. In the application of this 
technic to subtractive processes, the number of constants is so great 
that the reproduction may arbitrarily be made correct at several 
points within the boundaries of the realizable color solid. 

It may be added by way of conclusion that the requirements of the 
theory herein set forth are inescapable. They are the direct con- 
sequence of the characteristics of the visual processes of the human 
observer. No three-color process can ever duplicate the energy dis- 
tribution of each point of the subject, but it can be made to duplicate 
the visual effect, provided the necessary conditions are satisfied. 
That the conventional color separation-negatives do not properly 
control the reproduction primaries has been given tacit recognition 
by the empirical attempts at "correction," such as masking. Al- 
though such methods of correction are incapable of satisfying the 
conditions for perfect color reproduction, the improvement resulting 
from their use seems to indicate the desirability of employing the type 
of correction that a rigorous analysis of the problem prescribes. 


1 MACADAM, D. L.: "The Fundamentals of Color Measurement," /. Soc. 
Mot. Pict. Eng., XXXI (Oct., 1938), No. 4, p. 343. 

2 JUDD, D. B.: "The 1931 (CIE) Standard Observer and Coordinate System 
for Colorimetry," J. Opt. Soc. Amer., XXHI (Oct., 1933), No. 10, p. 359. 

"Handbook of Colorimetry," The Technology Press, Cambridge, Mass. (1936). 

3 HARDY, A. C.: "The Theory of Three-Color Reproduction," /. Opt. Soc. 
Amer., XXVH (July, 1937), No. 7, p. 227. 


MR. KELLOGG: Does your statement that we should be able to get accurate 
reproduction with the existing primaries presuppose that you do not in any case 
have to deal with colors above a certain purity? 

MR. HARDY: This mathematical treatment takes no account of whether the 
color is realizable in practice or not. If the color is one falling outside the gamut 


that can be achieved with positive amounts of the three primaries, the mathe- 
matics would simply indicate the fact by a change in algebraic signs. In practice, 
one does not know how to use less than zero grams of a certain dye in making the 
color reproduction. Mathematically, on the other hand, the actual number of 
grams required to reproduce a color outside the existing gamut can be calculated 
as easily as in the case of a realizable color. 

MR. KELLOGG : You said quite definitely you could make perfect reproduction 
with existing primaries. 

MR. HARDY: One can theoretically achieve perfect reproduction within the 
permissible gamut. Outside the permissible gamut, negative amounts of the 
primaries must be used. 

MR. KELLOGG: We can not do that. 

MR. HARDY: That is correct; but I wish to emphasize that that assumption of 
readability does not enter into the derivation of the equations. 

MR. MAURER: Mr. Hardy has shown that the characteristics of the filters to 
be used on the three-color camera, in order to obtain perfect color reproduction 
with the assumed set of subtractive primaries, are characteristics that are not 
realizable in practice, for the reason that negative transmission values are required 
at certain wavelengths. Have any studies been made indicating whether or not 
it would be possible to choose other sets of subtractive primaries, perhaps having 
smaller regions of overlap, that would permit the use of taking filters not having 
these regions of negative transmission? 

MR. HARDY: These linear transformation equations show that one element 
in the reproduction cycle must be imaginary. You might make the observer 
imaginary, but I do not think that would be good for the box-office. If you want 
to design the system for a human observer as he exists today, then either the repro- 
duction primaries must be imaginary or the filters must be imaginary. I think 
the practical solution is to use real primaries and to employ procedures that 
simulate the effect of imaginary filters. 

MR. MAURER: My point was merely that today rapid progress is being made 
in the production of new synthetic dyes, and possibly if a theoretical reproduction 
dye were indicated, synthetic work would eventually produce that dye. 

MR. HARDY: I think not. The requirements would be that the dyes used in 
making the reproduction transmit less than no light at certain wavelengths. 

MR. KELLOGG: The tricolor stimulus values as given in the "Handbook of 
Colorimetry" and elsewhere are based upon three specified monochromatic 
primaries. I understand that you can choose and define the primaries in various 
ways, but a certain three are generally taken as the reference standard. As I 
recall, there is only one curve that dips much below zero, and that is the red. 
You showed here a set of equivalent curves for the primaries you were last dis- 
cussing, in which each of the curves show a big dip, down almost to 40 per cent 
negative. Do those represent the theoretically required amounts of the various 
colored lights in view of the fact that they were not monochromatic but each had a 
rather wide spread? 

MR. HARDY: The primaries in the colorimeter system that Mr. MacAdam and 
I both have employed here are not monochromatic. I would rather not go into 
the exact nature of the primaries in the system, for the reason that the primaries 
of the system of colorimetry are not involved in the results I reported. Color- 

342 A. C. HARDY 

imetry enters into this discussion merely as a means for expressing the fact that the 
color of the reproduction is to be like that of the original. The primaries used 
in the colorimetric system cancel out, provided the same primaries are employed 
in both cases. 

MR. KELLOGG: But were not those curves for a specific set of primaries? 

MR. HARDY: The filter transmission curves were for the specific set that had 
been exhibited in the preceding slides. I showed how, in a typical subtractive 
process, to identify the primaries which were energy distributions in the red, 
green, and blue; and then, using those primaries, showed what the filter curves 
must be if those primaries are to be properly controlled in the reproduction. 

MR. GOLDEN: We all know that the lighting in the theater auditorium has an 
effect upon the projected screen picture. How does the color theory apply to 
this effect? 

MR. HARDY: When I talk about color reproduction in the graphic arts and am 
asked, "What happens when you have three inks and they happen to be printed 
upon paper stock of different colors?" my answer is that you make the print 
on the stock you are going to use before you figure out what filters should be em- 

Now, of course, if different theaters use lighting systems that are sufficiently 
different, then it will be difficult to obtain release prints that look right in all 
theaters. It is possible to select one theater, make the tests under the conditions 
obtaining in that theater, and design the cycle so that it will be exactly correct. 
For other theaters modifications should theoretically be made at some point in the 

MR. GOLDEN: Don't you think we should go a step farther, and standardize 
the lighting of the theaters of the country? 

MR. HARDY: Yes. As the art advances, more and more attention should 
properly be paid to such questions. 


Summary. The modern science of color measurement had its origin in the 
searches of Helmholtz, Maxwell, and Grassmann in the years from 1852 to 1855. 
This science found no important practical application until the opening of the 
twentieth century when the (F. .) Ives colorimeter was applied to the measurement 
and specification of the colors of practical illuminants. In 1922 the Optical Society 
of America, through its Committee on Colorimetry, recommended data and technics 
for color measurement which were immediately adopted throughout the world, re- 
placing numerous unrelated, and often inconsistent, technics that had been developed 
to meet the insistent demands of various industries for color specifications. A set of 
data based upon the most recent researches was recommended by the International 
Commission on Illumination in 1931, and these more satisfactory data have in turn 
replaced the data and extended the unification of methods which orginated with the 
O.S.A . Report of 1922. 

Standard I.C.I, color specifications can be computed from spectrophotometric data. 
The fundamental relations that are used to define the quantities in terms of which 
colors are specified are most concisely expressed in mathematical formulas , which will 
be simply explained. As a matter of fact, short cuts based upon the standard I.C.I. 
1931 data have been developed in the past few years so that no acquaintance with any 
mathematics other than ordinary arithmetic is now necessary for the performance of 
any of the essential operations encountered in standard color measurement. A typical 
example will be exhibited, and the interpretation of the results in terms of the dominant 
wavelength, purity, and brightness will be made clear by use of the chromaticity dia- 
gram. The conditions required in order that the colors of two samples shall match 
under some definite illuminant are that the three quantities in terms of which the 
colors are specified must be the same for the two samples. 

The purpose of this paper is to describe a practical method for 
measuring colors. Consequently, the basic visual experiments that 
justify the use of the method will be mentioned only briefly. Such 
experiments are based upon the familiar fact that almost all the colors 
encountered in nature and in industry can be matched by mixtures 
of any reasonable set of three primary colors of suitable intensities. 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 14, 1938. Communication No. 669 from the Kodak Research Laboratories. 
** Eastman Kodak Co., Rochester, N. Y. 




[J. S. M. P. E. 

In 1930 the International Commission on Illumination adopted the 
results of accurate and extensive experiments of this kind and recom- 
mended a method, based upon normal human vision, by which the 
intensities of three mathematically convenient primary colors can 
be computed from the distribution of energy in the spectrum of the 
color to be measured. The standard primary colors can not be secured 

FIG. 1. Diagrammatic representation of a method 
for computing the tristimulus values X, Y, Z. 

in any instrument, but, nevertheless, the computed intensities are very 
convenient specifications of color. For instance, if the intensities 
of the standard primaries computed from the energy distribution of 
two sample colors are the same for the two colors, then these colors 
will appear identical. 

Fig. 1 illustrates the principle of the method of computation recom- 
mended by the International Commission. The curve in the upper 
left corner of the diagram represents the reflectance of a green object 
for every wavelength of the visible spectrum, from violet at the left 


to red at the right. Such a curve must be determined for every sample 
whose color is to be measured. The optical instrument used for the 
determination of this curve is called a spectrophotometer. There 
are many varieties of spectrophotometers, some of which employ 
human observers, while others use photoelectric cells. 

The color of the sample depends upon the reflectance curve and 
also upon the distribution of energy throughout the spectrum of the 
light-source that illuminates the sample. The curve in the upper 
right corner of Fig. 1 represents the distribution of energy in the 
spectrum of a standard source of artificial daylight. Such a distribu- 
tion curve must be known for each illuminant with reference to which 
colors are to be measured. The International Commission on Illumi- 
nation has published such data for three light-sources which are de- 
fined as standards for color measurement. Data for other light- 
sources have been published in many other places. When satisfac- 
tory data on the distribution of energy in the spectrum of a desired 
light-source are not available, the data must be obtained by use of the 
methods of spectroradiometry. These data *can not be determined 
with accuracy outside of a few elaborately equipped laboratories where 
a specialty is made of such measurements. 

The energy reflected by the sample at a given wavelength is the 
product of the values at that wavelength indicated by the upper two 
curves (Fig. 1), and is shown in the curve just below. The three color- 
mixture functions adopted by the International Commission on Il- 
lumination are represented by the curves labelled x, y, z. Light of 
each wavelength reflected from the sample contributes to each pri- 
mary of the color specification an intensity proportional to the product 
of the energy and the corresponding color-mixture function. The 
three curves resulting from these multiplications throughout the 
visible spectrum are shown in the lowest set of diagrams (Fig. 1). 
The areas under the curves are the totals of the contributions at every 
wavelength throughout the spectrum to the intensities X, Y, Z, of 
the standard primaries necessary to match the sample color. These 
intensities are called the tristimulus values of the color. 

Mathematically this procedure is represented by the integrals 

X = fR-E-~ X 'd\, Y = fR-E'~yd/\ Z = fR-E~z-d\ 

These integrals mean nothing more nor less than the arithmetical pro- 
cedures represented in Fig. 1. 







500 600 700 










500 fcOO 


FIG. 2. Example of the selected-ordinate method 
of computing tristimulus values: (Upper) X, (Center) Y, 
(Lower) Z. 




Another and more rapid method of computing the tristimulus 
values has been devised. This is known as the selected-ordinate 
method and consists in averaging the values that the reflectance 
curve of each sample attains at certain wavelengths, which have been 
published. The thirty vertical lines in Fig. 2 (a) are drawn at the 
wavelengths at which the reflectances should be read from the curve 
of the sample, and averaged in order to compute the tristimulus 
value X. The values of the reflectance at the wavelengths indicated 
by the vertical lines in Fig. 2(6) should be averaged in order to com- 
pute the tristimulus value Y. Finally, the values read from the 
curve of the sample of the wave* 
lengths shown in Fig 2(c) should 
be averaged to compute the tri- 
stimulus value Z. Transparent 
templates, on which lines are 
ruled corresponding to the verti- 
cal lines in Figs. 2 (a), (b), and (c) 
can be prepared, to be placed 
temporarily over any spectro- 
photometric curve drawn to a 
standard wavelength scale, as 
aids in computation. The three 
sets of wavelengths have been 
derived from the color-mixture 
functions, adopted by the Inter- 
national Commission and shown 
in Fig. 1, and from the energy 
distribution of the light-source. These wavelengths are tabulated 
in the Handbook of Colorimetry, 1 which describes in detail the 
entire procedure of color measurement. 

If the tristimulus values of one color are some fraction of the 
tristimulus values of a second color, then these colors will look alike, 
except that the first will be less bright. The brightnesses of all colors 
are measured by the second tristimulus value, Y, alone. The ratios, 

x - X/(X + Y+Z), y = Y/(X+Y+Z), % - Z/(X+F+Z) 

are called trichromatic coefficients, and are the same for all colors that 
differ only in brightness. Such colors are said to have the same 
ckromaticity, and the chromaticity can be represented by a point in 
the chromaticity diagram shown in Fig. 3. The value of z can always 



0.6 0.0 

D.e OA 


FIG. 3. Chromaticity diagram. 
Illuminant C (artificial daylight) has 
been used for the specifications of the 
white and green samples. 

348 D. L. MACADAM [j. s. M. P. E. 

be computed from the indicated values of x and y, since x + y + z = 
1 for all colors. The chromaticities at the various wavelengths of 
the spectrum are represented by the points on the curve. The chro- 
maticity of daylight is represented by the point near the center. The 
green sample used for illustration in Figs. 1 and 2 is represented by 
the point above the white point. The brightness, 19 per cent, of 
this sample relative to the brightness of a perfect white in the same 
illumination is written beside the point representing the chromaticity. 
The dominant wavelength, 526 imz, analogous to the artist's hue, is 
the wavelength at which the straight line drawn through the white 
point and the sample point cuts the spectrum curve. The purity, 
22 per cent, analogous to the artist's saturation, measures the dis- 
tance from the white point to the sample point as a fraction of the 
distance from the white point to the dominant spectrum color. 

Samples that should match in color should have the same tristim- 
ulus values. This condition can be satisfied without requiring that 
the energy distributions of the light reflected from the samples are 
identical. Samples that match in color will be represented at the 
same point in the chromaticity diagram and will have the same 
dominant wavelength and purity. Errors in color matching can be 
represented as distances in the chromaticity diagram, and can be 
analyzed into errors of dominant wavelength and of purity. 

After the presentation of the paper, a 450-ft. 16-mm. Kodachrome motion picture 
was shown entitled "Color Measurement and Its Application to Color Photography." 
This film demonstrated the details and use of the method of color measurement de- 
scribed in the paper. A glimpse of the final steps in the preparation of a three-color 
subtr active print served as an introduction. A modified General Electric recording 
spectrophotometer was shown in operation, recording the spectrophotometric character- 
istics of the colors of a chart and of a subtractive reproduction of the chart. Close-up 
scenes emphasized important details of the double-prism monochromator, of the photom- 
eter mechanism, and of the modified integrating sphere and sample holders. The 
computation of tristimulus values, using the selected-ordinate method, was demon- 
strated in detail. In this demonstration, the speed and simplicity of the computations 
and of the recommended computing equipment were made evident. The interpretation 
of the colorimetric specifications was demonstrated, making use of the chromaticity 
diagrams published in the "Handbook of Colorimetry." 1 All the colors of the original 
color-chart and of the photographic reproduction were represented as points on a 
chromaticity diagram. The separations between points representing corresponding 
colors of the original and the reproduction were pointed out and compared with the 
visually apparent errors of the reproduction. This comparison led to the conclusion 
that the representation of the colors on the chromaticity diagram furnishes an adequate 
and unambiguous representation of all the visually important color errors. 



1 Handbook of Colorimetry," The Technology Press, Cambridge, Mass. (1936). 


MR. RICHARDSON: Do those errors represent the differences between the 

MR. MACADAM: The errors represented were the differences between the 
colors of the original color-chart and the corresponding colors of the reproduction. 
The colors used in the chart were picked as representative colors, likely to occur 
in any scene. The other ends of the error lines were simply the colors we found 
to have been produced by the color reproduction process. Perfect color reproduc- 
tion would result in zero errors. Every color in the final color picture should fall 
on the same point in the diagram as the corresponding color of the original color 

MR. BAKER: In determining a color by dominant wavelength, purity, and 
brightness, has that method definitely ruled out the use of the trichromatic 

MR. MACADAM: I think not. We use dominant wavelength, purity, and 
brightness because they give us quantities that are more meaningful. It does 
not avail one much to know that a color is 35 per cent f reen plus 10 per cent red 
plus 5 per cent blue ; but if you tell him that a color has a dominant wavelength 
of 526 millimicrons, and if he is familiar with the appearance of the spectrum, he 
knows that the hue is a very definite type of green. If you tell him further that 
the color has a purity of 22 per cent, he knows that it is a relatively unsaturated 
green, as compared with the spectrum; and a brightness of 19 per cent indicates 
that it is a moderately dark green. Consequently, it is easy to interpret dominant 
wavelength, purity, and brightness. That does not mean we are going to carry 
out monochromatic colorimetry. We are going to use a spectrophotometer of 
some sort and compute the dominant wavelength, purity, and brightness as 
outlined in the paper. If we use any type of colorimeter we must use an observer 
who is in our employ, and we must not use very many observers; consequently, 
the values we get in visual colorimetry are subject to some uncertainty as to 
whether the observers are normal. 

MR. KELLOGG: How do you specify dominant wavelength when the hue is 

MR. MACADAM: The dominant wavelength of a purple is nonexistent, and 
we specify the wavelength of the complementary color ; for instance, the magenta 
has a complementary wavelength of about 520 millimicrons. That is the wave- 
length of the spectral color necessary to produce a neutral color in a color mixture 
with the magenta. If we extend a straight line from the point representing the 
magenta color through the white point, it will intersect the spectral curve at 
some wavelength, for instance, 520 millimicrons. That is the complementary 

MR. RICHARDSON: Suppose a colored film is to be shown to an audience; 
what would be the differences in reproduction with different light-sources; for 
example, low- and high-intensity arcs, Suprex, Mazda, and so on? 

MR. MACADAM: Fortunately there would not be any large difference. The 

350 D. L. MACADAM 

color of the screen where we expect a white image seems to establish a standard 
by which we judge all the other colors. The film we have just shown was pro- 
jected several weeks ago with a high-intensity carbon arc projector, and today 
with a high-efficiency tungsten lamp, and I can not notice any difference in thei 
colors. It is interesting and fortunate that the relative quality of the colors does! 
not seem to depend seriously upon the quality of the illuminant. 

MR. HARDY: Does not the difference in the reproduction correspond to observ- 
ing a magazine illustration under daylight and under tungsten light? The differ- 1 
ence in the quality of the light-source in that case is probably greater than whatj 
Mr. Richardson had in mind. 

MR. KELLOGG: Since the sensitivity of the eye to brightness goes up so radi- 
cally in the green as compared with the red and blue, why does not white light 
look green to us? 

MR. MACADAM : That is a question that must be answered by a rather philo- 
sophic argument: White is the appearance of the stimulus to which we are most 
accustomed, such as daylight. All other colors have hues with respect to this 
most familiar (i. e., "colorless") stimulus. 

MR. RICHARDSON: Theaters are now projecting much colored film, and I 
certainly feel that projectionists and exhibitors should be informed of the differ- 
ences in color reproduction with the various kinds of light-sources in use. 

MR. MACADAM: I think it is rather generally expected that there will be 
differences. Whether they are important depends upon the observer, and I 
think we had better let the color-film people decide what light-source is best for 
the films resulting from each particular process. 

MR. KELLOGG : Can we at least say that the complete spectrum must be pretty 
well represented to get satisfaction; in other words, that there must not be any 
bad "holes" in the spectrum? 

MR. MACADAM: I am afraid the questions are getting beyond the scope of 
my investigations. 

MR. JONES : I think under certain conditions, at least, one can see the difference 
between, let us say, high-intensity arc and tungsten projection of some colors. 
The adaptation of the eye, while it is great, is not under all conditions sufficient 
to compensate for this difference in light-source quality. Commercial organiza- 
tions working on the development of color-films are studying the problem. 


Summary. Soon after sound reproduction in auditory perspective was demon- 
strated over telephone circuits between Philadelphia and Washington in 1933, ex- 
perimental sound pictures in auditory perspective were made at the Bell Telephone 
Laboratories' sound picture laboratory. Listening tests showed that they distinctly 
enhanced the illusion that the sound originated at its apparent source on the screen 
and they strikingly improved the feeling of spaciousness and reality. The auditory 
perspective effect is not primarily dependent upon perfect synchronism of the two 
sound-tracks required, nor on frequencies above the present commercial range. Exist- 
ing equipment can be converted to project sound pictures in auditory perspective with" 
out great difficulty. 

An auditor at the theater knows by his sense of hearing as well as 
by sight when an actor moves about the stage, and he can tell in what 
parts of an orchestra the various instruments are playing. Each of 
his ears hears sound from a slightly different direction, and he has 
learned by experience to associate the intensity and quality with the 
direction of origin of the sound. In a sound picture theater, on the 
contrary, the sound always comes from one fixed source, namely, 
the loud speakers behind the screen. This makes the reproduction 
resemble sound heard when an auditor listens directly to speech or 
music with only one ear. Under these conditions the perception of 
direction is seriously impaired. 

It has been shown 1 that reproduced sound can be made to appear 
to move from one side of a stage to the other by connecting two or 
more independent sets of loud speakers by separate circuits to sepa- 
rate microphones. That this method gives startling effects was dem- 
onstrated in 1933 when symphonic music was transmitted by such 
means over telephone lines from Philadelphia and reproduced in 
Washington. In these experiments the sound was picked up by 
three microphones placed near the front of the stage at Philadelphia. 
Each microphone was connected by a separate telephone circuit to a 

* Received June 4, 1938. 
** Bell Telephone Laboratories, New York, N. Y. 


352 F. L. HUNT [j. s. M. P. EJ 

separate set of loud speakers at Washington. With this arrangement! 
the audience was able to locate sounds from different parts of the 
orchestra and there was a feeling of spaciousness which gave the 
reproduced music a remarkable sense of reality. 

This perspective effect still persists if two microphones are used 
instead of three. In such case the middle microphone is omitted, 
and the remaining two are placed several feet apart in front of the 
orchestra. The output of each microphone is then amplified sepa-| 
rately and applied to a separate set of loud speakers located behind a 
screen at positions corresponding to those occupied by the micro- 
phones on the stage where the sound originated. 

The application of this multichannel method of reproduction to 
sound pictures requires in principle only the introduction, between 
the microphones and loud speakers, of recording machines to store 
the sound and reproducers to project it. Means for keeping the 
cameras and sound recorders in synchronism obviously have to be 
included. These facilities were available in the Bell Telephone Labora- 
tories' sound picture laboratory and an investigation was presently 
begun into the possibilities of this multichannel method. 

To study some of the effects that can be achieved, a series of ex- 
perimental sound pictures was recorded in auditory perspective. 
Several scenes were made in a sound picture set built of reinforced 
plywood flats like those commonly used in commercial sound studios. 
In accord with the usual practice the set had three walls. It was open 
in front and above to provide easy access for the cameras and to per- 
mit lighting the scene. Two electrodynamic microphones were used 
to record the sound. They were located about ten feet apart at the 
front of the set in positions that were found by listening tests to cover 
the set most uniformly These listening tests were carried out, and 
the sound was monitored during recording, by diverting part of the 
output of each microphone to a separate loud speaker located in the 
monitoring room associated with the stage. The output of each mic- 
rophone was connected by a separate channel to a standard film-re- 
cording machine. The two recording machines and the camera that 
photographed the action were synchronized by a standard Western 
Electric interlock system. 2 The sound records and the picture were 
originally recorded on separate films but afterward the picture and 
one sound-track were printed on one film in accordance with standard 
practice. The second sound-track was printed on another film. 

The sound picture scenes recorded were selected primarily to de- 


termine how faithfully the sound appeared to localize itself at its 
apparent source on the screen, and included the following scenes : 

(1) A person walking about the set from side to side, front to back, and for- 
ward again, speaking as he walked. 

(2) A banjo player walking about the stage while playing. 

(3) A banjo and saxophone, played alternately on opposite sides of the stage. 
(4} A piano played on one side of the stage. 

To reproduce the records two standard sound picture projectors 
were used, coupled by a flexible shaft to keep them in synchronism. 
The combined picture and sound-track were projected by one ma- 
chine and the second sound-track by the other. The output from 
each sound-track was amplified by a separate amplifier and supplied 
to a separate loud speaker. Western Electric cone speakers were 
used for most of the tests but in some cases high-frequency units were 
added. It was found, however, that the latter were not necessary to 
produce the auditory perspective effect. The loud speakers were lo- 
cated behind the screen near the right- and left-hand edges, and about 
half-way up from the bottom of the screen. Tests were also made 
with the loud speakers just outside of the screen and again about five 
feet away at each side. Neither of these positions gave as satis- 
factory an illusion as when the speakers were behind the screen, al- 
though the difference was not great when they were just outside. 
In some of the experiments low-pass filters, cutting off frequencies 
above 7000 cps., were connected in the loud speaker circuits to 
determine whether the auditory perspective effect depended upon 
the presence of frequencies above the 7000-cps. limit. It persists 
without them. 

The recordings were reproduced before several groups of observers, 
who, in a blind test, were asked to distinguish between the auditory 
perspective records and one or more of the following conditions : 

(1) The output of one of the two auditory perspective sound-tracks applied 
to a single loud speaker in the usual location. 

(2) The output of the two sound-tracks combined electrically and projected 
through a single loud speaker located behind the screen at the center. 

(3} The output of one sound-track applied simultaneously to the two loud 
speakers one at each side of the screen. 

(4) The output of the two sound-tracks combined electrically and projected 
from the two loud speakers. 

The tests were made by switching back and forth quickly between 
the conditions mentioned above and requiring the observers to de- 

354 F. L. HUNT [j. s. M. P. E i 

cide which condition prevailed at the moment. In most of the! 
tests two conditions were compared at a time, but in some instances! 
there were three. An audible signal was used to indicate that ap 
change was about to be made because the action on the screen con-| 
tinued without interruption. To assure an unbiased decision, how-i 
ever, the change signal was sometimes given without changing thel 
sound circuit. 

Comparisons were made also between the auditory perspective! 
recording of the first scene and one recorded by present commercial} 
methods with a single microphone located at the center of the stage. 
Quick shifts from one condition to the other could not be arranged for} 




Circuit Number of tions 

Test Observers Combinations Observations Correct Kind of Record 

1 A 2T-2S vs. IT-IS 15 100 Piano 

2 A 2T-2S vs. 1T-2S 16 8 1\ Speech- walking 

13 100 ( Banjo-walking 

4 100 1 Saxophone and banjo 

23 96/ Piano 

3 B 2T-2S vs. IT-IS 16 100 Piano 

4 B 2T-2S vs. 1 T-2S 20 100} Speech-walking 

8 50 ( Banjo-walking 

17 82 j Saxophone and banjo 

14 93 / Piano 

this part of the test because equipment was not available to project 
two pictures and three sound- tracks simultaneously; nevertheless, 
the auditory perspective recordings were preferred by all who heard 
the comparison. 

Experimental Results. The results are summarized in Tables I and 
II, where a letter is used to designate each of the seven observers. 
The circuit combinations are indicated by the number of sound-tracks 
(T) and loud speakers (S) used. For example, 2T-2S is the auditory 
perspective condition. 2T comb. -2 S means two sound-tracks com- 
bined electrically and applied to two loud speakers. The first table 
gives the per cent of correct observations and the second the per cent 
of correct choices for each circuit combination as they were played in 
succession. In tests 1 to 4, 7 and 8, the observers were told which 
combination was to be tested and were asked to indicate which one 

Oct., 1938] 



prevailed each time after the signal for the change was given. In 
tests 5 and 6, the three combinations used in each test were assigned 
numbers and then played successively at random. At each change 
the operator announced the number of the combination being switched 
in at that time, and after the test: each observer indicated the com- 
bination that he thought corresponded to the given number. 


Per Cent 







































2T comb.-2S 




2T comb.-lS 








2T comb.-2S 




2T comb.-lS 




Kind of Record 

Test Observers 





The tables show that the ability to distinguish between the audi- 
tory perspective condition (2T-2S) and either single loud-speaker 
reproduction from one sound-track (IT-IS) or single sound-track re- 
production from two loud speakers (1 T-2S) is of high order. When 
three conditions are imposed, as in the last four series, the number 
of errors is larger but still small enough to indicate that the effects 
are real and can not be explained as selection by chance. 

To show the effect of imperfect synchronization of the films the 
experiment of displacing one sound-track relative to the other was 
tried. As the displacement increased, an increase in the apparent 
reverberation of the sound occurred. This became obvious with a 
displacement of between one and two frames. When increased to 
four frames the effect was very obvious, and when the difference be- 
came eight frames the time lag was sufficient to give a distinct echo. 

356 F. L. HUNT [j. s. M. P. E.| 

Synchronism was maintained within a quarter of a frame, that is, I 
within one sprocket hole, when the sound-tracks were printed. 

It was agreed by those who heard these auditory-perspective sound I 
pictures that they distinctly enhanced the illusion that the sound 
originated from the source shown on the screen and that the sound t 
appeared to follow the image of the source as it moved. There was 
striking improvement in the feeling of spaciousness and reality, that 
is, the feeling that the sound originated in an actual room of three j 
dimensions. In previous auditory-perspective demonstrations fre-l 
quencies up to 15,000 cps. have been reproduced, but these experi- 
ments show that the effects still persist strongly when combined with 
motion pictures if frequencies up to only 7000 cps. are used. 

Since these experiments were carried out the art has been advanced 
by others. A public demonstration of sound pictures incorporating 
these ideas in practical form was given by Electrical Research Prod- 
ucts, Inc., at Bell Telephone Laboratories in 1937. 3 In these tests 
two sound-tracks were recorded simultaneously on a single film in the 
space ordinarily occupied by one sound-track. For this purpose a 
light-valve with two pairs of ribbons was used. One pair was ac- 
tuated by current from the channel at the right side of the stage and 
the other by the channel at the left. To reproduce the records the 
outputs of the two sound-tracks were picked up by a double photo- 
electric cell, each unit of which was connected to a separate ampli- 
fying system and to separate loud speakers. Each loud speaker 
comprised two units : a cone with a box baffle to radiate the low fre- 
quencies, and a multicellular horn for frequencies above 300 cps. 
The range radiated was from 50 to 8000 cps. 

The pictures shown included that of a large orchestra, which gave 
the audience an opportunity to observe that the sounds from the 
various instruments emanated from the positions where the instru- 
ments appeared in the picture. In another scene the sound of a 
ping-pong ball striking the bat or table passed from side to side as 
the ball was struck back and forth. A third scene started with an 
unlighted screen from which noise and voices came as the actors 
apparently stumbled about in the dark. Later a third actor ar- 
rived. As he turned on the lights, the picture of a somewhat dis- 
ordered living room appeared upon the screen. This gave the audi- 
ence an opportunity to compare the apparent origins of the sounds 
occurring at the moment with the actors' actual positions in the 


These demonstrations and those previously described show that 
sound pictures in auditory perspective can be added to present-day 
sound picture equipment without great difficulty and that they dis- 
tinctly enhance the realism of the presentation. The practical ap- 
plication of the method gives promise of being another significant 
step in perfecting the new art that has played so large a part in revo- 
lutionizing popular entertaiment during recent years. 


1 JEWETT, F. B.: "Perfect Quality and Auditory Perspective in the Trans- 
mission and Reproduction of Music," Science, 77 (May 12, 1933), No. 2002, p. 435. 

STEINBERG, J. C., AND SNOW, W. B.: Electrical Engineering, 53 (Jan., 
1934), No. 1, p. 12. 

Sound Motion Pictures (Including Stereophonic)," /. Soc. Mot. Pict. Eng., XXX 
(June, 1938), No. 6, p. 666. 

2 STOLLER, H. M.: "Synchronization and Speed Control of Synchronized 
Motion Pictures," Trans. Soc. Mot. Pict. Eng., XII (Sept., 1928), No. 35, p. 696. 

3 MAXFIELD, J. P.: "Demonstration of Stereophonic Recording with Motion 
Pictures," /. Soc. Mot. Pict. Eng., XXX (Feb., 1938), No. 2, p. 131. 



Summary. The use of electrical networks with recording and reproducing systems 
to accomplish beneficial results has been steadily increasing. Two types of networks 
are in general use, namely, wave-filters and attenuation equalizers. This paper dis- 
cusses in some detail the use of these networks with sound systems as reflected by 
present practices and later presents practical data for engineering the networks with 
a minimum of time and effort. The uses to which attenuation equalizers are put 
divide these networks into two general classes: first, fixed equalizers to provide fixed 
equalization for sound channels; and, second, variable equalizers to provide means 
for varying at will the relative amplitudes of the frequency components of sound 
signals. Although the means for engineering variable networks is far from being ideal, 
the review given in the paper of present practices should be valuable. 

Electrical networks such as wave-filters, attenuation equalizers, 
transformers, etc., are devices used as links in transmission systems 
for altering in some specified manner the transmitted electrical signals. 
Networks of this sort have been important parts of signal-transmis- 
sion systems for some time. In the communication field, for in- 
stance, many of the facilities in daily use would be impossible without 
such networks. In fact, realization of the commerical applications 
of networks by the communication industry is mainly responsible 
for the great amount of effort put forth to perfect the devices. 

At the time sound with motion pictures became commercially 
practicable, the development of networks had reached an advanced 
stage, making them directly available for use in the new industry. 
But new fields of endeavor require new methods of design and applica- 
tion. Such has been the experience in sound pictures. The technic 
of using networks with sound recording systems differs from that of 
using them with communication systems. Progress has been made 
toward applying networks to sound picture purposes but much yet 
remains to be done. This paper outlines some of the applications of 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 19, 1938. 

** Metro-Goldwyn-Mayer Pictures, Culver City, Calif. 


networks to sound picture work and gives some useful data especially 
arranged to meet the needs of studio sound departments. 

Sound originates from its source in the form of pressure variations 
in the air. The microphone, when properly placed, converts these 
acoustic variations into corresponding electrical variations which, 
when amplified, may be recorded on film. The simplest form of sound 
is a pressure wave varying sinusoidally with time. Complex waves, 
such as speech, music, etc., consist of large numbers of these simple 
components variously arranged with respect to amplitude, phase, 
time spacing, and time duration. The frequencies involved may 
range anywhere between twenty cycles per second and twenty 
thousand cycles per second. For speech and music these components 
consist of constantly shifting fundamental frequencies and their 
harmonics. Sound, then, is identified by the frequency components 
contained in the pressure wave. Any change made in the components 
changes the character of the sound as identified by the ear in the same 
manner as if the signal were emitted in the changed form initially. 

Electrical networks when arranged for use with sound systems are 
provided with a pair of input terminals for connecting to a system to 
receive energy, and a pair of output terminals to permit delivery of 
the modified signal back to the system. A signal in traversing the 
system from the input terminals to the output terminals can be modi- 
fied by the network in only a few ways. For instance, (1) the signal 
can be delayed in time by means of delay networks, (2) the relative 
phase relation of its frequency components can be altered by net- 
works known as phase correctors, (3) the signal can be decreased in 
volume with the use of attenuators, (4) the band of frequencies freely 
transmitted can be restricted to some definite limits by means of 
wave-filters, and (5) the relative amplitudes of its frequency com- 
ponents can be altered to effect a change in quality by means of net- 
works known as attenuation equalizers. Ordinarily the first two of 
these items are not of value in sound-picture work the first for the 
reason that time-delay by means of networks is too costly for the 
benefits received, and the second because phase correction of the type 
easily obtained with networks is not usually needed in sound work. 
The other networks, attenuators, attenuation equalizers, and wave- 
filters are used quite freely. 

As already mentioned, an attenuation equalizer is a network 
whose attenuation loss, over a given frequency range, varies with 
frequency in some desirable manner. This means that if a number of 

360 H. R. KIMBALL [J. s. M. P. E. 

frequencies of given amplitudes are simultaneously impressed upon 
the input terminals of an equalizer, the relative amplitudes of these 
frequencies will be changed when delivered to a load connected to the 
output terminals. The manner in which this change takes place is 
determined and can be controlled by the design of the equalizer. In 
sound picture work, the frequency range required extends from about 
40 or 50 to 7500 or 8000 cycles per second. This is called the 
transmission band. Equalizers for sound work then, are usually 
arranged to render a specified transmission characteristic in this 
range and little attention is given to what they do outside the range. 

Wave-filters provide the means for defining the recorded band; 
that is, they freely pass the above-mentioned frequency range and 
considerably attenuate other frequencies. The filters used in sound 
recording and reproducing channels are either of the low-pass or the 
high-pass type, there being little need for band-pass designs. 

Two general types of such networks are used in sound systems; 
that is, fixed networks and variable networks. By a fixed network 
is meant one whose transmission characteristic can not readily be 
changed; while a variable network is one provided with controls 
for varying its characteristic over a prescribed range. Fixed net- 
works are usually used with recording and reproducing equipment to 
compensate for any unavoidable distortions occurring, for various 
reasons, in the equipments, and to provide the fixed transmission 
characteristics that have been found to produce the best average 
product with the recording and reproducing equipments available. 
These characteristics for the different parts of a system may or may 
not be linear, depending upon the equipment limitations. Variable 
type networks or "patch-in" networks are usually concentrated al- 
most exclusively at the re-recording mixer positions, where the sound 
quality for the complete picture can be made uniform and sound 
effects rehearsed and altered as desired to obtain the best overall 

Recording Networks and Complementary Recording. The networks 
used in the original recording of sound are few in number and simple 
in construction. They often consist of a high-pass filter of one or 
two sections having a cut-off at about 60 cps., and a low-pass filter 
with a cut-off at about 7500 cps. These define the recording band 
from the frequency standpoint. The high-pass filter is to remove 
excessive stage boominess in a low-frequency range that is otherwise 
not important. The low-pass filter removes unimportant frequencies 

Oct., 1938] 



in the upper part of the frequency range. In the case of variable- 
density recording, this is an important function as it prevents over- 
loading and perhaps breakage of the light-valve in the vicinity of 
valve resonance. 

Recently a method of recording known as complementary* 
recording was put into effect at one major studio, requiring the 
use of one equalizer in the recording circuit to pre-equalize the 
recorded material, and another in the reproducing circuit to post- 
equalize this circuit in a complementary manner. Fig. 1 shows 
the recording characteristic obtained with the pre-equalizer and 





FIG. 1. 


Complementary recording. 

I the reproducing characteristic derived from the post-evualizer. 
When these two equalizers are used in this manner, the overall 
amplitude-frequency characteristic is unchanged because of the com- 

: plementary nature of the equalizers, the amplitude distortion in- 
troduced by the pre-equalizer being compensated for by the post- 
equalizer. Referring to Fig. 1, it will be noted that the pre-equalizer 
has an insertion loss of about 12 db. at 100 cps., 6 db. at 1000 cps., and 

* Because of the necessity of employing a post-equalizer in the reproducing 
system, complementary recording can not as yet be used for release prints. It is 
the hope that joint action to provide post-equalizers for all theater equipment 
will soon be possible. 

362 H. R. KlMBALL [J. S. M. P. E. 

very little loss at the high frequencies. In general, most of the transi- 
tion from 12 db. loss to db. loss occurs in the frequency range from 
300 to 3000 cps. The half-loss frequency of 1000 cps. is one of the 
design parameters of the equalizers. 

It is well known that a large part of the energy content of sound 
signals lies in the low-frequency range, say from 200 to 500 cps. 
Insertion of the above-described pre-equalizer into a normal recording 
channel without any change in the channel gain removes a large part 
of the signal load from the recording mechanism and the film, leaving 
the high-frequency content at approximately the same level. Be- 
cause of the removal of the low-frequency load, it is possible to in- 
crease the recording channel gain, thus increasing the recorded level 
of the high-frequency content and achieving a greater ratio of high- 
frequency signal to static surface noise ; that is, an increase in noise- 
reduction. Subsequent post-equalization does not destroy this in- 
creased noise-reduction because of the concentration of surface noise 
in the upper part of the frequency spectrum. 

Complementary recording also effectively eliminates "breathing," 
by which is meant the audible change in surface noise caused by the 
recording mechanism's being placed, by the noise reduction equip- 
ment, in the proper position to handle the signal. For normal re- 
cording the greater the signal volume the greater is the breathing, 
and since most of the signal energy lies in the low-frequency range, 
much of the breathing is produced by the lower-frequency components 
of the signals. It may be mentioned also that masking is a factor in 
breathing because when breathing is produced by a high-frequency 
signal, the surface noise is masked somewhat by the signal. Use of 
this type of pre-equalizer in the recording circuit therefore con- 
siderably reduces breathing because the recording mechanism is not 
modulated nearly as much by the low-frequency signal content. 

Complementary recording has also a few other associated benefits. 
For instance, intermodulation, causing spurious signal products, is 
reduced because of the lower level of the low-frequency components. 
Bias current components also are reduced for the same reason. In 
addition, wave-top clipping on steep wave-fronts, caused by the 
sluggishness of the noise-reduction equipments, is reduced. Still 
again, complementary recording provides greater margin of operation 
for the low-frequency components thus permitting occasional high- 
peaked signals to be handled with less overload. This is equivalent 
to an increase in volume range. 



In conclusion, it may be mentioned that complementary recording 
iccomplishes beneficial results for two basic reasons; first, the energy 
iistribution of acoustic signals lies in the lower part of the audible 
'requency spectrum, and, second, film surface noise is concentrated 
n the upper part of the frequency range. Reducing the level of the 
ecorded signals in the low-frequency range does not materially in- 
crease the signal-to-static surface-noise ratio in this same range, but, 



FIG. 2. 

Mixer circuit; 12-db. insertion loss (x = constant- 
resistance patching points. 

:>n the contrary, permits the over-riding of surface noise in the upper 
i frequency range. This, in connection with the reduction in breath- 
ling, decreased intermodulation effects, and the other items outlined 
! above constitute the benefits of this method of recording. 

Re-recording Arrangements. Re-recording rooms are usually ar- 
i ranged to have acoustic characteristics approximating those of aver- 
ige large motion picture theaters. This is necessary in order that 
; the re-recording mixers may adjust the sound quality and effects to 
produce the results desired when the record is reproduced in an 
average theater. Facilities are made available to permit joining 

364 H. R. KIMBALL [j. s. M. p. : 

the sounds from a number of sound-tracks, by means of a mixir 
table, to form one composite signal for monitoring and for re-recor< 
ing. Combining as many as eight tracks into one is not unusual, ar 
sometimes as many as twelve sound-tracks are joined. The mixir 
table is arranged so that each track may be dealt with separately < 
a number of tracks as a unit. 

Fig. 2 shows a mixing table arrangement permitting joining 
maximum of sixteen sound-tracks into one. Patching points a: 
available for the insertion of networks into the circuit of each soum 
track or at points where the sound-tracks are combined in groups < 
four. At each point where networks may be inserted, the circu 
impedances are equal resistances in the two directions, so that ar 
inserted network will operate between its designed resistance 
Where constant-resistance networks are inserted, this permits tl 
operation of any number in tandem without altering the characteri 
tics of the individual networks. This constant-resistance featu: 
at the patching points is made possible by the design of the mix 
coil, which may be designed to combine any number of circuits 
multiples of two into one channel. For instance, the sixteen-positic 
mixer of Fig. 2 could be handled by means of only one mixer co 
For flexibility of patching, however, the four-position coil seen 
more practicable. The insertion loss through the mixing circuit 
Fig. 2 is 12 db., or 10 log 16. This is the minimum loss that can 1 
obtained for the sixteen positions. 

The above-described mixing circuit is only one of a number of a 
rangements that can be used. Usually it is not necessary to pro vie 
as many as sixteen mixer positions. Some saving in equipment cs 
be achieved where a smaller number of mixer positions is satisfactory 
The general requirements are to provide minimum insertion los 
flexibility of patching, and constant resistance at the patching point 

A large variety of fixed and variable-type equalizers and filte 
are available for re-recording. There are at the present time no stan< 
ard networks in use by all the studios although many of the studic 
have quite similar equipments. 

Reproducing Networks. As in recording systems, the networl 
required in reproducing sound are few in number and simple in desigi 
Most reproducing systems employ only two networks: one a lo\ 
pass filter to suppress system and surface noise lying above the us< 
ful signal frequencies, and the other a dividing network for use wit 
the loud speaker system. The low-pass filter is often of the variab 


ype, permitting adjustment of its cut-off to suit the theater in which 
; is installed. Information is given later in this paper regarding the 
arious types of dividing networks. In addition to these types of 
etworks some reproducing systems eniploy equalizers for compen- 
ating for loud speaker characteristics, but these are of special design 
nd will not be discussed here. 

Miscellaneous Networks. In addition to the above-mentioned net- 
works, which are more or less standard, a number of different types 
f networks are used in various test equipments, and for special 
urposes such as for equalizing microphones of different types, for 
ompensating for room effects, etc. These are usually of conven- 
onal design and present no great difficulties.* 
Attenuation Equalizers. As already mentioned, an attenuation 
qualizer is a four-terminal network whose attenuation loss, over a 
iven frequency range, varies with frequency in some desirable 
lanner. This means that if a number of frequencies of given am- 
litudes are simultaneously impressed upon the input terminals of 
n equalizer, the relative amplitudes of these frequencies will be 
langed when delivered to a load connected to the output terminals, 
he manner in which the change takes place is determined and can 
e controlled by the design of the equalizer. In practice the shapes 
equired of the insertion-loss curves of equalizers appear to vary over 
| wide range. Actually, many equalizer problems are but duplica- 
tions of others with different values assigned to the network con- 

' From the great amount of work that has been done on the design 
f attenuation equalizers a number of general circuit arrangements 
nave emerged that have proved to be the most satisfactory for general 
ise. The network engineer does not necessarily restrict himself to 
he use of these few types but they do represent a large part of his 
:it of tools. These equalizer circuits are designated in the following 
nanner : 

>1) Series impedance type. 
#) Shunt impedance type. 

3) Full series type. 

4) Full shunt type. 

5) rtype. 

6) Bridged- T type. 

7) Lattice type. 

* Some of the information from this point on is summarized from data in 
'Motion Picture Sound Engineering." (Cf. ref. 1, p. 380.) 



Network Type 


[J. S. M. P. 

Not Not 2f) , ^o + 

Constant Constant. R 


~* Shunt 
4 Imp. 

Not Not ?n , RQ + 

Constant Constant 8 Z 2 



o 9n , -o 

Constant 20 log 





Not 2f) . 

Constant 20 log 

20 log 



2 o log ^ 



(1) Z!Z 2 = -Ro 2 for all networks 

(3) Working Circuit = 

FIG. 3. Fundamental equalizer types. 


Fig. 3 shows these seven equalizer types in schematic form. For 
these circuits, it is assumed that the system impedances to which 
connection is made for operation are equal resistances of RQ ohms. 
In sound picture work R Q has values of the order of 500 ohms, 200 
ohms, 16 ohms, and various other resistances. The variable char- 
acteristics of the equalizers are made to depend upon two general 
impedances denoted in the circuits as Z\ and Z 2 and defined as being 
inverse to each other with respect to the line resistance RQ] that is, 

It is noted that the insertion-loss formula, as expressed by the 

T T RQ + Zl RQ + Z 2 

I.L. = 20 log -- = 20 log - 
AO Z 2 

is applicable to each of the equalizer types. This means that an 
insertion-loss characteristic obtained with one of the equalizer types 
can be duplicated by any of the other types. The formula shows 
also that the shapes of the insertion loss curves of the equalizers 
of Fig. 3 are determined solely by the inverse arms of the networks 
as represented by impedances Zi and Z 2 . This feature makes it 
practicable, in a design problem, to determine the circuits of the 
inverse arms independently of the equalizer types with which they 
are to be used. 

Since the same insertion loss characteristic may be obtained with 
any of the equalizers of Fig. 3, the question naturally arises as to the 
advantages of one type over another. In this connection it will be 
noted from the figure that the input and output impedances for the 
types are not the same. For the first two types, both these impe- 
dances vary with frequency ; for the next two types one impedance is 
constant and the other one varies; and for the last three types, both 
Zi2 and Z 34 are constant. Then, for instance, where a constant- 
impedance network is needed, one of the last three types must be 
used. Commercial features also help in making this decision, as 
one would select the type easiest to build which meets the circuit 

The impedances Zi and Z 2 may take any form of circuit arrange- 
ment so long as they are inverse to each other. In practical work 
a few common circuit arrangements are sufficient for most purposes. 
Fig. 4 shows eight pairs of simple inverse circuits for which data 



[J. S. M. P. E 






>> * = . 






FIG. 5. Insertion loss No. 1 inverse arms. 

5.0 TO 10O 

FIG. 6. Insertion loss No. 4 inverse arms. 

370 H. R. KlMBALL 

are given in this paper. Each of these pairs may be used with an> 
of the equalizers of Fig. 3, provided the modifications shown foi 
the various types in Fig. 3 are made; that is, 2Z b Zi/2, Z 2 /2, 2Z 2 

The insertion-loss formula for each pair of inverse arms and the 
general form of the insertion loss characteristic are also given (Fig. 4) 
It will be noted that the insertion-loss curves for the first foui 
pairs of arms range from zero to infinity. This is because these in 
verse arms are purely reactive, and their impedances vary betweer 
zero and infinity. For these four pairs of inverse arms the fre 
quency f a is defined as the frequency where a 3-db. insertion losj 
is obtained. This frequency f a is a design parameter. The symbo 
f r is used to designate the resonance or anti-resonance frequencies ol 
the arms, where of course, such points exist. Because of the inverse 
relation between Z\ and Z 2 , the resonance frequency of one is the 
anti-resonance frequency of the other. The symbol a is used to de 
note the ratio of f r to f a , that is, a = f r /f a . In cases where f a mighl 
be either greater or less than / , the lower frequency is selected foi 
f a so as to make the value of a always greater than unity. 

The networks obtained by the use of the last four pairs of inverse 
arms have no infinite insertion-loss points, but vary between zerc 
and some finite value determined by the symbol k. That is, the 
maximum insertion loss is 20 log k, and therefore k is a design pa 
rameter that becomes known when the maximum loss desired for 
network is known. The symbol f b is used to indicate the frequency 
where one-half the maximum loss is secured or 10 log k. The symbol 
b denotes the ratio f r /f b , and again f b is always selected to be less 
than f r so that b is always greater than unity. 

The values assigned to k, f r , f a , and / determine the electrical 
elements for the inverse arms. Having decided upon a particulai 
pair of these arms, they may be used with any of the equalizer types 
of Fig. 3. The formulas for computing the elements from a knowl- 
edge of R Q , k, f r , f a) and/ are given in Fig. 4. 

For design work it is useful to have curves available to aid ir 
selecting the fundamental design parameters. These have beer 
prepared to cover a wide range of applications. Figs. 5, 6, 7, 8, and 
9 are examples of such curves. The recent book 1 on sound engineer- 
ing contains a complete set of design charts and tables as well as 
material showing the preparation and use of the formulas. These 
data are too voluminous to be given here. 

FIG. 7. Insertion loss No. 7 inverse arms. 

0.2 0.3 0.4 0.5 0.7 1.0 2.0 3.0 40 SO 7.0 10.O 

FIG. 8. Insertion loss No. 7 inverse arms. 

12 0.3 04 OS 07 10 20 30 4.0 5.0 70 K 

FIG. 9. Insertion loss -No. 8 inverse arms. 

372 H. R. KlMBALL [J. S. M. P. E. 

Wave-Filters. Electric wave-filters, like attenuation equalizers, 
are four-terminal networks having a pair of input terminals and a 
pair of output terminals. Between the input and output terminals 
is an orderly array of electrical elements arranged so as to produce a 
specified insertion-loss characteristic when connected between the 
proper terminal impedances. Unlike equalizers, resistive elements 
are excluded from wave-filters; only inductive and capacitive ele- 
ments being used to interconnect the input and output terminals. 
The reason for the exclusion of resistive conductors is contained 
in the purpose of a filter; i. e., to transmit, without appreciable loss, 
all frequencies of the transmission band, and to attenuate by a pre- 
scribed amount frequencies lying outside this band. If resistive 
elements were used attenuation would result within the transmission 

Electric wave-filters consist usually of a number of filter sections 
of unit four-terminal networks connected in tandem on a matched- 
impedance basis to form the complete filter. It is not necessary that 
a filter consist of more than one section, but usually the transmission 
characteristic desired is such as to require the use of multiple sections. 
In this respect filters are different from equalizers, where in a great 
many cases, the desired equalization curves may be secured without 
tandem operation of sections. 

Conventionally designed wave-filters seldom provide constant im- 
pedances at their terminals over the operating frequency range, and 
for that reason it is usually not possible to achieve a match of im- 
pedance between the wave-filter and the system to which it is con- 
nected, even though the impedances of the latter are constant resis- 
tances. In general, the terminal impedances of filters are largely 
resistive in their transmission bands and reactive in the attenuation 
ranges. In addition, in the transmission range the resistive char- 
acteristics vary with frequency, especially in the cut-off region. 
While various methods are available of stabilizing these impedances 
to almost any desired precision, most filters, as arranged for com- 
mercial purposes, provide some mis-match at their terminals. The 
insertion loss of a filter takes into account these terminal effects and 
for that reason it is important in operating filters to make sure that 
the proper connecting impedance conditions are obtained. 

Although wave-filters transmit the frequencies of their transmis- 
sion band without appreciable attenuation loss, they do shift the 
relative phases of all the frequencies. This is an inherent feature 



of filters that can not be avoided, although in some cases means are 
available for controlling the phase-shift characteristic so as to mini- 
mize its effect upon transmission. In many transmission systems, 
the effect of phase-shift is not of sufficient magnitude to require cor- 
rection, while in certain types of systems corrective means must be 
employed. In sound pictures it has not been found necessary to 
correct for the phase-shift in the filters generally used. 





FIG. 10. Filter transmission bands. 

For design and nomenclature purposes, wave-filters are classified 
into four types, in accordance with their attenuation characteristics: 

(1) Low-pass filters. 

(2) High-pass filters. 
(5) Band-pass niters. 

(4) Band-elimination filters. 

For low-pass filters, the passing band includes the frequency range 
from zero frequency to some finite frequency. For high-pass filters 
the passing band covers the range from infinite frequency down to 
some finite frequency. A band-pass filter transmits a definite band 
of frequencies, and attenuates frequencies lying outside the band. 
A band-elimination filter transmits all frequencies except a band of 
frequencies to be attenuated. Band-elimination filters, although 
forming an integral part of classified filter theory, are seldom used, 
for the reason that there is very little commercial need for filters 
having that type of attenuation characteristic. Fig. 10 shows the 
transmission and suppression ranges for the different types of filters. 

Figs. 11 and 12 show the low-pass and high-pass filter sections most 
commonly used in practice. Filters consisting of tandem sections 
are obtained by joining together the various sections shown on a 
matched image-impedance basis. The terminals of the sections 
having like image impedances are indicated in Figs. 11 and 12. 2 

374 H. R. KlMBALL 

Dividing Networks. In the design of linear sound reproducing 
equipments where it is desired to reproduce faithfully tones from about 
50 cycles per second to about 8000 cycles per second, it is common 
practice to divide the frequency range into two or more parts and 
provide one or more loud speakers for each of these frequency ranges. 
The speakers employed for the different bands are, of course, dif- 
ferently designed, each speaker being particularly suitable for its 
own band. Since it is not possible to design loud speakers that will 
faithfully and efficiently reproduce frequencies in one preassigned 
band, and sharply attenuate frequencies outside the band, it is neces- 
sary to supply an electrical network between the final power am- 
plifiers and the loud speakers to deliver the correct frequency band 
to each set of loud speakers. These networks have acquired the 
name of "dividing networks." 

In practice, loud speaker systems may be of the two-way or three- 
way types. Because of the preeminance of the two-way system, only 
networks for use with such systems are discussed here. For the two- 
way system the speakers handling the lower frequencies are termed 
the low-frequency, or low-range, speakers. In like manner, the 
speakers that reproduce higher frequencies are called the upper- 
frequency speakers or upper-range speakers. For each of the two 
frequency bands one speaker unit or a number of speakers are ar- 
ranged in series-parallel combinations to secure the proper combined 

Dividing networks are not usually of the sharp cut-off type; that 
is, they are not arranged to transmit uniformly frequencies of a given 
band and then attenuate sharply all other frequencies. Rather, they 
transmit the band frequencies almost uniformly and gradually slope 
off, thereby providing a certain amount of overlap between the as- 
signed frequency ranges. While theoretically it may seem desirable 
to arrange dividing networks to cut off sharply, from a commercial 
standpoint the sharpness of cut-off is necessarily a compromise be- 
tween expense and effectiveness. For well designed loud speaker 
systems, the rate of change of attenuation should be sufficient at 
least to suppress objectionable irregularities in the response of one 
horn in its transmitting range because of sound coming from the other 
horn in its suppression range. From an analysis of a large number 
of speaker systems it appears that dividing networks should provide 
at least 10 to 12 db. of attenuation one octave away from their cut- 
offs. In considering networks having greater rates of change of 



o -^ 






*; i 

T o 






FIG. 11. Low-pass filters. 











VI - 

m = Vl-(/K// c ) 2 

Z l = RoVl-(fc/f)* 

VI ~ 

, = ^ 










FIG. 12. High-pass filters. 



Parallel Type 
Dividing Network 

Series Type 
Dividing Network 

1 vlAJULr T 



L, L 2 

OJJLtU ^) O . fl ft * " 


Speakers C, Z 

L 4 




: 4 

' fr T 






1. Frequency 

L C L ' 





L 'l 



FIG. 13. Filter-type dividing networks. 












AN& (b) OF FIG. 4 
SOVER - 321 







24 o 








* "5 



















16 ? 




NETWORKS (c) AND (d) OF FI6. 4 







) 2 



f.4 3 






* a 












FIG. 14. Transmission loss of filter-type dividing networks. 

378 H. R. KlMBALL [J. S. M. P. E. 

attenuation it should be remembered that increased attenuation is 
accompanied by increased loss in the transmitting ranges, which, 
for high-powered systems at least, is to be avoided. Costs also may 
mount unreasonably if a large amount of filtering is employed. For 
these reasons, and considering the magnitude of the irregularities 
that one speaker produces in the transmitting range of the other, it 
appears that few dividing networks should employ more attenua- 
tion than about 18 db. per octave. 

In a two-way system, the frequency at which both sets of loud 
speakers receive equal amounts of energy is called the cross-over 
point. In other words, the cross-over point is the point of separation 
between the two bands of frequencies. In developing loud speaker 
systems a trial cross-over point is usually arbitrarily selected, keeping 
in mind the characteristics of the upper- and lower -range speakers 
that are to be used, and the costs and other items. This point is 
then later moved one way or the other if found unsatisfactory when 
the system is operated as a whole. 

A two-way dividing network consists of a low-pass filter and a 
high-pass filter designed to operate from a common source at their 
input terminals. Two methods are in general use for connecting the 
filters in series or in parallel at their input terminals; namely, (1) 
the filter method; and (2) the constant-resistance method. Each 
of these methods is capable of good results. The filter method is 
the more commonly used probably because it is better known, and 
is somewhat more flexible in design. 

Fig. 13 shows circuits for four filter type dividing networks. Cir- 
cuits (c) and (d) are the more commonly used in practice. The 
symbol RQ denotes the resistance of the speakers connected to the 
low-frequency and high frequency terminals. The symbol f a denotes 
the cross-over frequency. The transmission characteristics for these 
networks are shown in Fig. 14. 

Fig. 15 shows four types of constant-resistance dividing networks. 
For these networks, circuits B and D are the more commonly used. 
Here again the symbol RQ is used to denote the speaker resistances 
and f a indicates the cross-over frequency. These networks measure 
a constant resistance at the input terminals when the proper loads 
are connected to. the speaker terminals. Fig. 16 shows the transmis- 
sion characteristics for the different circuits. 

Variable Networks. Networks whose transmission characteristics 
may be smoothly varied over a wide range by means of a single 

Oct., 1938] 





-co r $ R 



R O =LOW- 




Circuit A 




Circuit B 




\F o 

f f. . 





Circuit C Circuit D 

L, - -^ L, = ^ L , = V2L, 

Ci = V2C 

f a = cross-over frequency of network 
FIG. 15. Constant-resistance dividing networks. 

FIG. 16. Constant-resistance network insertion loss; (-4) net- 
work of circuits A and C, Fig. 15; (B) networks of circuits B and D, 
Fig. 15. 

380 H. R. KlMBALL 

control are especially useful in the re-recording work of motion pic- 
ture studios. At the time, however, the methods available for engi- 
neering such networks are not all that can be desired, with the result 
that occasionally the re-recording mixers are somewhat handicapped 
in their technic. The requirements for variable networks are three 
in number: namely, (1) minimum loss for the result accomplished, 
(2) constant-resistance impedances at the input and output terminals, 
and (3) a smoothly variable transmission characteristic. 

The networks now in use usually attempt partially to meet these 
requirements by a variety of methods. One common method is to 
provide constant resistance and minimum loss by varying the trans- 
mission characteristic in a step-by-step manner. This is done by 
multiple switching arrangements to connect to tapped electrical 
elements. This method results in a complicated mechanical and 
electrical structure and often introduces noise in the circuit while 
the step changes are being made. In addition, it is often necessary 
to compromise on the network design because of the added mechani- 
cal difficulties. 

Another method in common use is to sacrifice the constant-resis- 
tance and minimum-loss features in order to provide a smoothly vary- 
ing transmission characteristic by means of potentiometer-type vari- 
able resistors inserted somewhere in the circuit. Aside from the 
above-mentioned sacrifices the chief difficulty with this method is that 
flexibility of design is not realized, with the result that even the 
transmission characteristic is a compromise. The greatest advantage 
of this method is simplicity of mechanical and electrical structure. 

It is hoped that in the not too distant future a more suitable design 
technic will be made available for this purpose. Whether this will 
require the development of entirely new network structures or altera- 
tion of existing structures the writer is not able to say. 


1 "Motion Picture Sound Engineering," D. Van Nostrand Co., New York, 
N. Y. (1938); ed. by Academy of Motion Picture Arts & Sciences, Hollywood, 

2 Ibid., pp. 260-272. 


Summary. Multiple-channel recording is a device for achieving flexibility at the 
time of dubbing or re-recording orchestral music presented as such in the picture. If 
one could predict for the music and sound departments which portions of the orchestra 
would be seen from which angles in the final picture, or if the editing could be com- 
pleted before the music was recorded, there would be less merit in multiple-channel 

The reverse is true: The music is recorded first, the musicians photographed later, 
synchronizing their movements to a play-back of record. Meanwhile, the pictorial 
treatment has taken partial shape in the minds of producer and director. Still later 
it takes final shape in the hands of the film editor. Sound and action are then placed 
in the hands of the sound department for dubbing, but it is then too late for more than 
an ineffectual raising and lowering of volume. The violins or the woodwinds can not 
be lifted above the surrounding sections to match a close-up of the picture. 

The multiplicity of sound-tracks (recorded, of course, in advance of the photography) 
provides the dubbing mixer with the means of easily blending a final sound-track that 
will be wholly in keeping with the final edition of the picture. The application 
of this method to the recent production "100 Men and a Girl" is described. The use 
of "close-mix" tracks, separate vocal tracks, etc., in conjunction with multiple record- 
ing is also described. 

In the case of expensive sound sources, such as symphony or- 
chestras, it has long been the practice to make two or more identical 
records from a given source of sound by employing two or more re- 
cording machines each of which is ordinarily energized from some 
common point in the amplifying channel but which might equally 
well be assigned a complete channel of its own. In contrast to this 
procedure the term "multiple-channel recording" as used in this 
paper, refers to the use of a number of recording machines each as- 
sociated with a separate and complete sound channel to make simul- 
taneous records of different aspects of a complex sound source. 

A simple form of multiple-channel recording has been practiced in 
Hollywood for a number of years wherein the vocal effort of a soloist 
is recorded through one channel while simultaneously the accompany- 

* Presented at the Spring, 1938, Meeting at Washington, D. C. 
** Universal Pictures Corp., Universal City, Calif. 


382 H. G. TASKER [j. s. M. P. E. 

ing orchestration is recorded through another channel. This pro- 
cedure affords several advantages which will be mentioned later, but 
among them is one that inspired the much more extensive multiple- 
channel recordings that form the principal subject of this paper. 
This advantage lies in the ability to postpone the "balancing" (that 
is, the adjustment of relative loudness) of the two principal sound 
elements (vocal and instrumental) until the picture has reached its 
finishing or dubbing stage. 

The magnitude of this advantage can be best appreciated when it 
is remembered that musical numbers, especially vocal ones, are al- 
most always pre-recorded. In this method the sound-track is re- 
corded before the picture is photographed, the latter taking place by 
the process known as "playback" wherein the vocalist sings a duet 
with herself and each of the instrumentalists plays a duet with him- 
self as the original record is played back on the set during the photo- 
graphing. This is repeated for as many different angles, close-ups, 
long shots, etc., as are desired, and as many takes of each as may be 
required to obtain the desired degree of perfection. Following the 
photographic step the scene is edited by intercutting the various 
takes and angles until the best possible entertainment or story values 
have been incorporated in the scene. 

Now, if all our producers, directors, musical directors, and music 
mixers were supergeniuses, then the music mixer might, by con- 
ferring with the others, successfully visualize the exact form that the 
final edited scene should take, and hence could balance the sound at 
the time of recording for a perfect interpretation of the scene. Not- 
withstanding the claims of studio press agents to the contrary, no 
such degree of genius exists in Hollywood, and every attempt to 
balance the vocal and instrumental portions of recording for the final 
editing has proved in some measure disappointing; hence the de- 
sirability of postponing the balancing until all the creative work 
of producer, director, and editor has crystallized in the edited film. 
This obvious benefit to the rendition of vocal numbers is realized with 
very little complexity of the recording system since only two separate 
channels are required, one for the voice and one for the orchestra. 

Extension of this idea to the rendition of strictly orchestral music, 
as for example, a number by a famous band or symphonic orchestra, 
involves much more complexity because it is desired to feature on the 
screen from moment to moment various sections of the orchestra, 
pr even individual performers, and to provide acoustic balance ap- 


propriate to the scene in all cases. To Leopold Stokowski, famed 
conductor of the Philadelphia Symphony Orchestra, goes credit for 
the first application of this method to tjie rendition of large orchestral 
numbers in the motion picture production One Hundred Men and a 
Girl. He was not without opposition from skeptics in both technical 
and non-technical ranks, including those who questioned whether 
the re-recording machinery could ever synchronize the resulting six 
or eight sound-tracks to the required degree. 

Preliminary study convinced us, however, that this objection was 
not serious. We had had extensive experience with a technic known 
as "close mixing," in which a microphone is supplied for each principal 
section of the orchestra for example, violins, cellos, woodwinds, 
brasses, etc. the several microphone outputs being fed to a mixer 
panel where they are suitably balanced before the recording. In this 
method the directional properties of ribbon microphones are employed 
to give best possible separation between the several sections, yet it 
is obvious that the violin microphone will pick up some of the energy 
from each of the other sections and each other microphone will do 
likewise. Since the microphones are placed at an average of eight 
feet apart there is considerable delay between the arrival of the violin 
sounds at the violin microphone and its arrival at the other micro- 
phones. This is identical in effect to the slight errors of synchroniza- 
tion that might occur in multiple-channel recording and results in a 
reverberant quality but which is never as severe as is the reverberant 
effect when recording with a single microphone placed far enough 
away to be equidistant from most of the sections of the orchestra. 

It is obvious that the degree of synchronism need only be compar- 
able to that of the several microphones placed throughout the orches- 
tra. The available degree of synchronism being approximately Y 2 
frame, corresponding to about 25 feet of air distance, we concluded, 
and experience later proved, that no difficulty would be encountered 
from this source. 

In connection with these recordings for One Hundred Men and a 
Girl there was more than ordinary need for such an arrangement to 
permit postponing the balancing of the orchestra: the recordings 
were to be made in April for a picture that was to begin production 
in May ; they were to be recorded in Philadelphia for a picture to be 
photographed in Hollywood ; and the scenes in which they would be 
employed had not yet fully crystallized in the minds of the writers and 
producer. With these facts in mind, we requested the RCA Manu- 

384 H. G. TASKER [j. s. M. P. E. 

facturing Company to provide at the Academy of Music in Phila- 
delphia eight separate channels. Six were to be used for the simul- 
taneous recording of the several sections of the orchestra, one to 
record the orchestra as a whole from a pair of overall, or "long-shot" 
microphones, and one to record the voice of Deanna Durbin with 
orchestral accompaniment. In view of the considerable expense of 
assembling the talent and equipment for these recordings it seemed 
the better part of wisdom to provide one more channel equipped 
with six microphones and a conventional mixer panel so that our 
usual close-mixed track could be made simultaneously, as a protec- 
tion in case anything went wrong with any other part of the system. 
Each of the separate channels consisted of a microphone, the custom- 
ary amplifier, and gain controls, and the recording machine ; and was 
manned by a mixer and a recordist. The close-mix channel had six 
microphones and a six-position mixing panel controlled by Mr. Bern- 
ard Brown, head of the music and dubbing section of Universal's 
Sound Department, who was sent to Camden as our representative 
for the whole recording operation. The six microphones of the "close- 
mix" channel were placed as close as possible to the six "separate 
channel" microphones, respectively. With these arrangements all the 
symphonic and two vocal numbers for the picture were recorded. 

The great merit of multiple-channel recording is especially well 
demonstrated in this motion picture by the rendition of Liszt's Second 
Hungarian Rhapsody on the staircase of Stokowski's home. The 
director, Henry Koster, chose to portray a great deal of this scene in 
a series of "approach" shots to the several sections of the orchestra 
and to various principals of the story. When the resulting edited 
picture was experimentally projected with the conventional close- 
mixed track it was found to be quite "flat" and unconvincing. It al- 
most completely lacked the inspiring vigor that it later acquired as a 
result of appropriate mixing from the individual tracks of the multi- 
ple-channel recording. 

While multiple-channel recording, as just described, can yield re- 
markable results in connection with the rendition of orchestral num- 
bers, the number of such scenes that occur in the course of a year's 
production in any one studio is relatively small and it could not be 
expected to find a very extensive field of application unless it were to 
prove materially helpful in the more common type of musical 
numbers, namely, vocal. However, the instrumental accompaniment 
/or vocal numbers has little need of the discriminative balancing of 


sections from moment to moment because its level must be low 
enough to accompany the voice of a singer suitably and because in- 
dividual sections of the orchestra are rarely featured on the screen 
during such a number. 

For these reasons the simple form of multiple-channel recording 
mentioned earlier has been adopted as the standard method of re- 
cording vocal numbers at this studio except for the inclusion of a third 
channel. On this third channel is produced a combined vocal and 
orchestral track which serves a double purpose. It affords protec- 
tion in the event of failure of either of the other two tracks, and 
provides an immediately available work-track in which the two ele- 
ments are reasonably well blended. 

To simplify the operations of this three-channel system the mixer 
dial of the vocal channel appears on the same panel with the six 
mixer dials of the orchestral channel. Their outputs are led sepa- 
rately through their respective channels to their respective recording 
machines, but by means of bridging amplifiers the third channel plus 
the mixer's monitor circuit are energized from the combined outputs 
of the vocal and orchestral microphones. 

In addition to the advantage already described for such a system 
a second important advantage is often gained in that it is not neces- 
sary to obtain simultaneously a perfect orchestral recording and a 
perfect vocal recording plus a perfect balance of each with respect to 
the other. If, for example, a vocalist is not adequately rehearsed or 
becomes "out of voice" it is possible to make the instrumental track 
first and then dismiss the expensive orchestra (often $500 to $700 per 
hour) and arrange for the vocal recording on the following day or at 
any convenient time after a choice take of the instrumental track has 
been developed and printed. In this subsequent recording the vocalist 
hears the reproduced instrumental track through the headphones and, 
singing to this accompaniment, repeats the performance so often as 
necessary until a perfect vocal recording has been made. Especially 
in the case of young or nervous performers, the total absence of the 
orchestra and any accompanying high pressure often proves very 
helpful. Since the orchestral track is not being re-recorded at this 
time, but will be combined with the vocal track at a later date, ar- 
rangements are made to aid the mixer in his judgment of the vocal 
quality by introducing the desired level of the orchestra into his 
monitor through bridging amplifiers, so that his basis of judgment is 
almost identically the same as if the orchestra were present. 


J. L. BOON** 

Summary. A casual observer, looking over the existing standard amateur photo- 
graphic equipment, would probably be of the opinion that there is little need of altering 
a camera to do a special job. However, closer observation of the various problems that 
photography serves reveals that the standards of practice have been chosen merely to 
suit the needs of a common majority of users, and the minority are almost forgotten. 
Further observations show that an alteration to a standard camera to make it fit a 
specific purpose usually precludes its usefulness for many of the purposes for which 
it was originally designed, and also its utility for other special purposes. 

In this paper are made known some of the unusual adaptations of 16-mm. motion 
picture equipment, each to fulfill a definite purpose, and it is shown that industry is 
becoming more conscious of the utility of such photographic equipment as tools in 
solving some of its problems. 

A casual observer looking over the existing standard amateur 
photographic equipment would probably be of the opinion that there 
is little need for altering a camera to do a special job. However, closer 
observation of the various problems that photography serves reveals 
that the standards of practice have necessarily been chosen primarily 
to suit the needs of a majority of users. Usually an alteration to a 
standard camera to make it fit a specific purpose precludes its use- 
fulness for many of the purposes for which it was originally designed 
and also its utility for other special purposes. 

At one time some of the features now included on standard motion 
picture equipment, such as speeds other than normal, lenses of various 
focal lengths, variable shutter openings, etc., would have come 
within the scope of this paper. The incorporation of these features 
in standard cameras, however, has not decreased the inflow of requests 
for equipment for special uses. 

Extension of Camera Speed Range. Fortunately, the simplest 
form of alteration is the one most often requested, that is, the ex- 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 19, 1938. 

** Eastman Kodak Co., Rochester, N, Y. 




tension of the speed range. At one end of the range, exposure in- 
intervals of as long as one per day would be useful. If the long in- 
terval is also a fixed interval, a simple method of achieving the result 
is to let a continuously running synchronous clock motor wind a 
small coiled spring one turn per fixed time interval, at the completion 
of the turn releasing the spring, which then drives the camera shutter 

FIG. 1. 

Electric release and control for making exposure 
at variable intervals. 

and pull-down through one revolution, exposing and advancing the 
film. The motor may also close a light circuit for illuminating the 
subject during the exposure interval. If greater accuracy of timing is 
required than such an arrangement permits, the motor is stopped after 
one turn of spring winding, and an external impulse releases the 
spring for driving the camera and also starts the spring-winding mo- 
tor. Another method proposed for limited use is to enclose the camera 
and subject in a light-tight box, moving the film continuously or 



[J. S. M. P. E. 

intermittently. The exposure is made by flashing a light by means 
of an accurate external source. The resulting film would probably 
be unsatisfactory for motion picture projection, but individual frames 
could be viewed or enlarged. 

A variable-interval device operating automatically has been manu- 
factured for the Cine Kodak Special (Fig. 1). Timing is accomplished 
by means of a condenser discharge operating a relay, which in turn 
sends an electrical impulse to a solenoid on the camera single-frame 
shaft. The camera spring furnishes the driving power for the mecha- 
nism; the solenoid merely allows the single-frame shaft to make 
one or one-half a turn. Batteries are included with the control box, 

Plane 1 

Point 1 

FIG. 2. Plan for taking pictures of take-off and land- 
ing of airplanes, showing image displacement for two dis- 
tances (not drawn to scale). 

eliminating a further source of power. A secondary interval multi- 
plier increases the interval range at the longer end. 

Although there are many uses for cameras with long intervals be- 
tween exposures, the majority of requests are for cameras that operate 
at speeds greater than normal. Many motion picture cameras, other 
than those for sound, will operate at 64 pictures per second. For 
most motion analysis this speed merely indicates what might be 
learned if higher camera speeds were used. It is not very difficult to 
drive a camera at 120 frames per second, but driving it on batteries 
with a speed variation of less than 0.5 per cent is somewhat more 
difficult. It was done, however, by using a synchronous motor for 
driving the camera; and by changing the gear ratio between the 
motor and the camera, various camera speeds were attained, each 
within close tolerance. 


Photographing Airplane Take-Off and Landing. A method was de- 
vised for the Department of Air Commerce for measuring the distance 
and altitude of an airplane as it makes a take-off or landing. 1 Two 
Cine Kodak Specials sixty feet apart, or multiples thereof, were used 
to photograph the runway (Fig. 2). It was found that pictures taken 
at the rate of four per second gave satisfactory readings. This speed 
could be attained readily and synchronously by using a solenoid 
release on each camera and operating both on a single impulse from 
the control box. Matched lenses of 2 1 /2-hich focal length were used. 
The cameras were slightly "toed in" to converge in field at a distance 

FIG. 3. Side view of twin projectors used in taking 
data from pictures of the take-off and landing of air- 

of 1600 feet for the 60-foot base line, 3200 feet for the 120-foot base 
line, etc. 

It was necessary to build a special twin projector for taking read- 
ings from the film, since slight displacements of the airplane images 
on the two films had to be measured at the same time (Figs. 3 and 4). 
A separate projector is used for each roll of film of the pair, but 
both films are advanced frame by frame by a common drive, so that 
right and left pictures move in synchronism after they have once been 
set in matched pairs. Geneva drives are used and the film is held in 
the gate between glass plates which separate as the film is moved. 
The lens on one projector is movable horizontally and that on the 
other vertically so that corrections may be made for slight film dis- 
placements. All the controls are operated from the viewing side 

390 J. L. BOON [j. s. M. P. E. 

of the two adjacent translucent projection screens. The two images 
of the airplane taken at the same time gradually separate as the air- 
plane moves farther away. This separation is measurable directly 
in feet by means of a special transparent scale at the projection 
screen, to a distance of about 2500 feet with a 60-foot camera base 
line. From the distance reading, the altitude is also read directly on the 
scale. The camera base line may be increased so that distances of 
more than 2500 feet are readable on the scale. 

A " Shutterless" Camera. In making a motion picture camera for 
recording a subject of low intensity, such as the x-ray image on a 

FIG. 4. Screen and direct-reading scale for measuring 
altitude and distance of airplane. 

fluorescent screen, it is not only necessary to use the fastest lens and 
film available, but also a shutter of almost 100 per cent efficiency; 
that is, no shutter at all. This means that the pull-down time must 
be less than 5 per cent of the exposure time to eliminate travel-ghost. 
A spring was attached to the pull-down claw in such a way as to ac- 
celerate its film pull-down motion. An overrunning clutch was at- 
tached to the pull-down shaft to prevent any chance of reverse mo- 
tion of the pull-down. The shaft is independent of the drive in its 
forward motion, but the motion ceases at completion of the pull- 
down stroke; until a driver, which runs concentrically with the pull- 
down shaft and which turns at a definite speed, catches up with it and 
rotates it through the remaining half of the stroke. This driving also 
stretches the spring to full tension so that it is again in position to 


accelerate the pull-down of the film when the driver rotates the pull- 
down shaft a little beyond dead center. The tension in the spring 
determines the pull-down speed, and the exposure time is approxi- 
mately the reciprocal of the number of pictures taken per second. It 
was thought that 8 pictures a second would be the most satisfactory 
compromise, and in order to project these pictures at the taking speed 
without flicker, a projector was altered to give 48 shutter interrup- 
tions at a film speed of 8 frames a second. This could be done without 
destroying the balance between blurring and stuttering of the screen 
image, since the motion photographed is somewhat slower than 
normal. Alterations in the projector involved doubling the shutter 
shaft speed with respect to the pull-down up-and-down motion and 
a change in the in-and-out pull-down motion to decrease the time that 
the pull-down claw is engaged with the film. 

Abnormal Picture Proportions. Requests for abnormal picture 
proportions have been few but are usually well founded. A recent 

FIG. 5. Stereoscopic pictures on 16- mm. film mounted in a cassette. 

one was for motion pictures on 16-mm. film with the height-to-width 
ratio changed from 3 X 4 to 4 X 3. This could be accomplished quite 
easily by photographing with the camera on its side. The problem of 
altering a standard projector to give an erect image was a bit more 
difficult. Prisms or mirrors in the optical path were tried and found 
satisfactory under laboratory conditions but were subject to strain, 
collected dust, and caused considerable loss of light. This led to 
trying the same trick on the projector as on the camera, that is, turn- 
ing it on its side. The lamp house was rebuilt so that the lamp 
burned in a vertical position, and the supporting base was remade 
to suit the conditions. In general, this has proved quite satisfactory, 
and it is thought that slight unsteadiness, which, of course, shows 
up horizontally instead of vertically, is less noticeable. 

The same customer requested also a means of photographing a 
subject, making several thousand small, still pictures in color in a 
short period of time, and projecting ten or twelve pictures of different 
subjects on a translucent screen with an automatic means of changing 

392 J. L. BOON 

the picture after a fixed time interval. Although these pictures were 
to be used as stills, it seemed necessary to take them in a motion 
picture camera, since they had to be made in a short period of time 
and were to be in color. The most satisfactory height-to-width 
ratio was found to be 3 to 2. On 16-mm. sound-film, the maximum 
width that can be used for pictures is about l / 2 inch, which would 
make the height about 2 x /2 frames. Allowing tolerance for mounting, 
a little more than three frames was desirable for each picture. With 
this much known, alterations on a Cine Kodak Special were begun. 
The aperture in the gate was increased in width and height, the pull- 
down stroke doubled, the sprocket speed doubled, and the shutter 
speed cut in half. With the increased angle subtended by the aper- 
ture from the shutter center, it was necessary to decrease the shutter 
opening. Exposure with the camera running at four pictures a second 
is about the same as with a normal 16-mm. camera at normal speed. 

Two cameras of this type were built to operate side by side from 
the same power source, doubling the output or making stereoscopic 
pairs. The film could be processed normally and the individual pic- 
tures cut to fit die-cast cassettes (Fig. 5). These cassettes hold ten 
pictures or five pairs of stereoscopic pictures, each stereoscopic pair 
being mounted with interocular separation. The cassettes then serve 
two purposes. They may be used in a simple stereoscope for single- 
station viewing, or projected singly upon a screen. The projector 
built for the latter purpose consisted of lamp house, condenser, and 
projection optics, translucent screen, and the cassette carrier and as- 
sociated mechanism. The mechanism allows each picture to be 
projected for about eight seconds and then advances the cassette 
holders for the next picture to be projected. 

The Eastman high-speed camera, 2 the race-timing camera, 3 and 
the associated rapid developing and enlarging unit 3 have already 
been described in the JOURNAL. 


1 "To End Guessing on Runway Lengths," American Aviation, 1 (July 15, 1937), 
No. 4. 

2 TUTTLE, F. E.: "A Non-Intermittent High-Speed 16-Mm. Camera," /. 
Soc. Mot. Pict. Eng., XXI (Dec., 1933), No. 6, p. 474. 

3 TUTTLE, F. E.: "Photographic Race-Timing Equipment," /. Soc. Mot. Pic. 
Eng., XXVII (Nov., 1936), No. 5, p. 529. 


C. E. IVES** 

Summary. In a previous paper a rack was described that provided for 
continuous motion of a 200-ft. length of motion picture film during processing but 
could be used with the rack-and-tank equipment. The purpose of this roller rack 
was to give a type of treatment in processing essentially similar to that given by 
a continuous machine while retaining the features of batch equipment that are 
helpful in experimental processing. 

The rack previously described included a built-in driving motor and reduction 
gear, an arrangement that was most feasible for a single unit. With more extensive 
use it became desirable to have multiple units operated from stationary drives at the 
tanks and at the loading and unloading stations. 

A new design has been worked out in which the weight of the rack was reduced 
greatly by the use of stationary drives. Further reduction in weight was attained 
by the substitution of tensioning springs for the weighted supporting beam associated 
with the movable lower shaft in the earlier model. This shaft was mounted upon the 
frame by lever arms in such a way as to use the torsional rigidity of the shaft itself 
to maintain it parallel to the upper shaft while allowing it the necessary vertical 

In an earlier paper 1 a rack was described which provided for con- 
tinuous motion of a 200-ft. length of motion picture film during proc- 
essing and which could be used with rack-and-tank processing equip- 
ment. The purpose of this rack was to facilitate the conduct of 
experimental work by the provision of a type of treatment similar to 
that given by a continuous processing machine with equipment 
which could be used under conditions of batch operation favorable to 
frequent change of developer and time of treatment. 

The film was carried in a helical path over a succession of rollers 
at the top and bottom of the rack, the upper and lower rollers each 
having a common shaft. In order to permit continuous motion in 
one direction, the film strands from the ends of the helix were joined 
to form a closed loop. The return strand so formed was located 

* Presented at the Spring, 1938, Meeting at Washington, D. C. ; Communica- 
tion No. 671 from the Kodak Research Laboratories. 
** Eastman Kodak Co., Rochester, N. Y. 




[J. S. M. P. E. 

along the bottom of the rack. Thus, starting at one end, the film 
reached the other end of the rack by following a helical path, turning 
around rollers along the top and bottom, left the last upper roller to 
go to the lower corner of the rack while making a quarter turn, tra- 
versed the length of the rack on the supporting rollers along the 
bottom, and then after making another quarter turn arrived at the 
starting point. The drive motor and reduction gear were built in. 

FIG. 1. Elevation of new roller type of developing rack. 

This rack was found to fill a definite need and consequently was 
used extensively. With an increasing volume of work it became 
necessary to have additional units in service. An opportunity was, 
therefore, presented for making certain improvements in design and 
reducing the weight of the rack. 

Desirable Features. After reexamination of the features of the 
existing rack, it was concluded to provide for a 210-ft. film length 
with the same film path, the completely submerged film path being 

A running speed of approximately 150 feet a minute was thought 
desirable in order to simulate continuous machine conditions and to 


obtain some improvement in development uniformity. The higher 
speed would also have the particular advantage with the roller rack 
of assuring greater uniformity of treatment throughout the 200-ft. 
length by increasing the number of times the whole path was tra- 
versed during development. 

With multiple-rack operation it would be practicable to install 
driving means at the processing tanks and at loading and unloading 
stations, thus making possible the removal of the drive from the rack 
with a considerable reduction of weight of the latter. Drives located 
at the processing tanks would be partly submerged in the bath so 
that the design would have to dispose of the problems of corrosion, 
contamination, and leakage. 

Accommodation for expansion of the film when wetted and pro- 
vision for redistribution of slack would have to be furnished by move- 
ment of one of the shafts in the vertical direction under tension, while 
it was maintained parallel to the other. The use of a slide or track 
for this movement should be avoided because of the friction intro- 

The rack frame should be rigid and light in weight and should 
have clean lines and an open construction favorable to quick drain- 
age of the solutions. The presence of mechanical parts other than 
the rollers within the film loops was considered sufficiently objection- 
able to warrant a redesign of the evener mechanism. 

In order to be used with existing tank equipment the rack should 
not exceed 2 inches in width and 54 inches in length. The height 
should be about 48 inches. The improved rack is illustrated in 
Fig. 1 and its features are explained by means of the figures and de- 
scription which follow. 

The Driving Shaft. In order to obtain a compact and simple drive 
unit it was decided to drive through the upper shaft and maintain 
the film loops taut by means of a spring-tensioned movable lower 
shaft. With the driving unit located at one end of the tanks near the 
top, it was necessary only that the upper shaft be extended slightly 
beyond the end of the rack and fitted with suitable means for engage- 
ment with the drive gearing. In order to obtain immediate starting 
and a simplicity of manipulation fitted to working in total darkness, 
direct engagement with the running drive was decided upon. A 
means of accomplishing this, described by White in an article on 
equipment for testing motion picture film, 2 was considered for the 
present purpose but did not lend itself well to use in the 2V4-inch 

396 C. E. IVES [J. S. M. P. E. 

space available. The design chosen consisted of direct engagement 
(radially) of two spur gears at a peripheral speed of about 200 feet a 
minute. Good service has been obtained with a 12-pitch, 22-tooth, 
V2-inch face gear of reinforced bakelite on the rack and a similar, 
slightly wider stainless steel gear on the drive. The bakelite gear has 
undergone some wear under this shock loading during ! 1 / 2 years of 
use but is still in service. Wear on the steel gear has been negligible. 
The upper shaft consists of a 1-inch outside diameter ground 
stainless-steel tube closed at both ends. It is supported by three 
plain bearings of reinforced bakelite which receive the required lubri- 
cation from the processing liquids. The bearings at center and right 
in Fig. 1 are for axial loads only, all thrust being taken by the bearing 
at the left. At this point the shaft diameter is stepped down to 7 /ie 
inch by means of an extension piece which is sweated into the tube. 
Beyond the bearing to the left is the bakelite gear which is held in 
position from one side by a pin through the shaft and on the other 
by a jam nut and lock washer. 

This end bearing is fastened by screws to a bracket on the frame. 
When the screws are loosened the shaft can be passed, with the 
gear in place, through an opening in the end frame member of the 
rack to permit removal of rollers at the opposite end of the rack. 
The bearing block is extended 5 /ie inch outside the frame, where it 
is turned to a cylindrical shape to act as a trunnion, by whose engage- 
ment with a guide plate on the drive unit the gear center distance is 

Film Supporting Rollers. In the model described previously, in 
which hard-rubber rollers were used, only one flange to the roller was 
used to save space. At the present time rollers are made of reinforced 
bakelite which is sufficiently strong to permit the use of much nar- 
rower flanges. This, in combination with other changes in the 
frame providing additional space, has made possible the use of 
double-flange rollers, with a resulting improvement in film guiding. 

All rollers are equipped with soft-rubber treads which eliminate the 
scratching usually seen along the perforation track of machine-proc- 
essed film. These treads grip the surface of the film support very 
strongly so that, when slack is being redistributed along the rack, 
any slippage must be between the rollers and the shaft. At the same 
time it is necessary to apply some driving force over and above that 
furnished by the friction between the rollers and the shaft. This 
additional friction is furnished by the use of six rollers with friction- 


drive pads of the type shown in Fig. 2. The pads are pressed against 
the shaft by the arcuate flat stainless-steel spring with sufficient force 
to require a tension of eleven ounces at the film line to cause slippage. 

The lower shaft rollers are similar to the remaining upper rollers 
except for the bore. 

The Lower Shaft. Differences in the expansion of various materials 
when wetted, as for example, coated film and uncoated leader, cause 
looseness of the film at one point or another along the rack. Re- 
distribution of this slack is brought about by compelling the lower 
shaft to remain parallel to the upper shaft while it moves up and 
down. If parallelism is maintained, then any slack which appears 
while the film is running is immediately redistributed, because the 
shorter strands receive the full tensioning force applied to the shaft. 

FIG . 2 . Drive roller with auxiliary friction pads. 

In the previous model the required downward force was provided 
by the weight of a heavy stainless steel beam which supported the 
shaft at three bearing points. Two extension coil springs of stainless 
steel supply the tension in the new model. The most suitable loca- 
tion for the springs is in the channel members forming the upright 
rack ends (Figs. 1 and 3). Here they are suspended from an ad- 
justable screw while the spring tension is transmitted to the movable 
shaft by means of a 7 X 7, Vie-inch diameter stainless-steel stranded 
cable. The cable is anchored to the frame just below the spring, 
passes over a pulley block suspended from the latter, from which 
point it goes to the bottom corner of the rack, and, after passing under 
a sheave, reaches a quadrant affixed to the movable lower shaft. 
This cable is strong, economical of space, and tolerant of slight mis- 

Mechanism for Obtaining Parallel Shaft Movement. With the elimi- 
nation of the lower shaft beam and the old type of parallel motion 
gear, both of which were formerly located above the lower shaft within 
the film loops, a new means of supporting the shaft and of effecting 



[J. S. M. P. E. 

parallel movement was required. It was found that the shaft itself, 
although so slender as to have little beam strength, was of suitable 
proportions to act as a quite rigid torsional evener. 

The operation of the evener is described conveniently by reference 
to Fig. 3, which shows schematically the lower shaft mechanism and 
spring- tensioning system. The shaft is clamped at three points in 
crank arms (see also Fig. 4) which pivot on three pins supported by 
the frame on a common horizontal axis. Downward pull to hold the 
film loops taut is applied by the cables which are fastened to the quad- 
rants associated with the cranks at the ends of the shaft. 

Vertical movement of the shaft 
caused by a change in the length 
of the film loops results in move- 
ment of the cranks about the 
pivots and a corresponding rota- 
tion of the shaft. Thus, if one 
end of the shaft is lowered slightly 
with consequent rotation about 
its axis and the other is held up 
by a shorter film loop, the tor- 
sional rigidity of the shaft tends 
to cause a corresponding rota- 
tion at the latter point as well. 
Rotational force at the attached 
crank causes, in turn, an in- 
creased downward tension upon 
the short loop and thus brings 
about the desired redistribution 
of the film on the rack. For a small displacement, the movement 
employed may be compared to that of a shaft carrying three pinions 
moving along racks. The rigidity of the stainless-steel shaft of 
3 /8-hich diameter is sufficient to transmit the 16-pound force through 
the length of 48 inches with less than 0.1 -inch vertical displace- 
ment. With this tension applied at each end, any slack is im- 
mediately redistributed. 

Bowing of the shaft is prevented by locating another crank and 
pivot at the midpoint which employs the torsional strength of the 
shaft in the manner described above to maintain the shaft at the 
point of attachment approximately in line with the shaft ends. With 
a 0.812-inch distance between crank centers and a vertical movement 

FIG. 3. Schematic representation 
of parallel movement mechanism and 
tensioning system. 

Oct., 1938] 



of about 0.923 inch, the lateral movement is only 0.144 inch. The 
spring design is such that the tension changes only 20 per cent with 
the full vertical movement of the shaft. 

The Return Path. As formerly, the path by which the film returns 
from one end of the helix to the other is located along the bottom of 
the rack. The seven supporting rollers are carried within the bottom 
frame member on shafts fastened to the sides of the channel by means 
of countersunk screws. For removal 
of the screws the shaft can be held 
by a pin inserted in a hole in the 
roller and shaft. 

The Frame. The frame is made 
entirely of 16-gauge stainless-steel 
sheet stock and comprises four prin- 
cipal members. These are of chan- 
nel form for the bottom and the 
two upright ends, and triangular for 
the top piece, providing for rigidity 
and convenience in lifting the rack 
from the tanks. These parts and 
the lower corner gusset plates are as- 
sembled by butt welding. Brackets 
are attached by spot welding. The 
weight of the frame was reduced 
slightly by punching out holes in the 
larger surfaces. The frame is suffi- 
ciently rigid for the mechanical 
movements employed. 

Drives on the Tanks. The tanks 
in which the rack is used have di- 
mensions of 60 inches in length, 54 
inches in depth, and either 6 or 10 inches in width. To avoid diffi- 
culties in alignment and to obtain a simple drive presenting a mini- 
mum contamination and corrosion hazard, individual splashproof 
motors were mounted on each tank (Fig. 5). The only points re- 
ceiving oil lubrication are the well guarded motor bearings. Direct 
speed reduction from the 1150-rpm. motor shaft to the 385-rpm. 
rack drive gear in the bath is obtained through a chain drive. 
A 9-tooth sprocket is mounted on an extension of the motor shaft. 
The Vs-inch, V2-inch pitch roller chain engages this and the 27- 

FIG. 4. Close-up of lower cor- 
ner of rack. 



[J. S. M. P. E. 

tooth sprocket on the drive gear. These parts are of stainless steel. 
The drive gear has a combination bushing and thrust washer of 
reinforced bakelite which runs on a stainless-steel stud with the proc- 
essing solution for lubrication. This gear is held in position by the 
stainless-steel apron which covers all of the moving parts and acts 
as a splash and safety guard. The apron is entirely open at the 
bottom to facilitate cleaning. 

Racks are guided into the tank (Fig. 6) by the strips welded to the 


FIG. 5. Drawing of drive unit on tank. 

face of the apron. Correct positioning of the rack gear relative to the 
drive gear is maintained by causing the rack trunnion to rest in the 
recess in a guide plate fastened to the apron. The rack is also sup- 
ported at the diagonally opposite bottom corner where a shelf is lo- 
cated a few inches above the tank bottom. Angular misalignment 
of the gears in the horizontal direction is limited by the rack guides 
at the opposite end of the tank to approximately 1 degree in either 
direction, which is acceptable for the purpose. Space is provided for 
temperature control pipes which enter back of the apron. 


The Loading Station. At another point in the developing room a 
drive is installed for running the rack while it is being loaded (Fig. 7) . 
In this case a reduction gear of conventional desfgn is used, since the 
corrosion and contamination problems are not severe. To facilitate 
locating the rack on the loading stand, guides are mounted behind the 
rack position near the drive and at the supporting shelf at the bottom. 

Loading is carried out by opening a splice in the leader with which 
the rack is always threaded when not in use, and then attaching the 
film to one of the ends. The drive is started, causing the film to be 
led onto the rack while the leader is taken up on a rewind at the point 

FIG. 6. Tank with rack in position. 

where it is leaving the rack. In this operation and later when the 
rack is being unloaded, a guide roller with soft rubber treads (visible 
at the top of the rack in Fig. 7) is brought into bearing against the 
edge portion of the film at the point where the leader or film is leaving 
the rack. This assures sufficient contact of the film with the roller 
on the rack to provide the necessary drive. The guide roller is carried 
by a resilient mounting which is slipped onto the upper frame member 
when needed. A friction hold-back on the feeding roll is adjusted to 
maintain enough tension in the entering film strand to prevent the 
lower rack shaft from rising or falling. Operation of the drive motor 
is controlled by a foot switch. The maximum loading speed is 200 
feet a minute. 

402 C. E. IVES [J. S. M. P. E. 

Splices are made by means of metallic clips put in by a hand-held 
device. Reasonably accurate alignment is required for proper run- 
ning of the film but perforations are not registered. 

The Unloading Truck.- The processed film is passed through a port- 
able pneumatic squeegee 3 and transferred to reels for drying. During 
this operation the rack is carried on a movable truck (Fig. 8) equipped 

FIG. 7. Rack threaded with film standing in the load- 
ing station. 

with a drive similar to that used on the loading station. As the film is 
removed leader stock is fed in from a stock roll carried on the truck. 
The motor is controlled by means of a portable switch cord which the 
operator can attach to his clothing. Running speed is limited to 100 
feet a minute or less by -the capacity of the squeegee. 

Operating Procedure. The loading operation is managed in such a 
way as to maintain the movable shaft in the upper half of its range of 


Positive, negative, and sound developers are used. Development is 
timed by the use of an electric darkroom clock with an error of less 
than 5 seconds. The rack is handled by two meri. The rack is con- 
tinuously driven in the stop-bath and fixing bath, but the film is ad- 
vanced on the rack only occasionally in the course of washing. 

When picture negative film is developed, there is a tendency to form 
airbells on the emulsion 4 at the point at which the bottom roller enters 
the developer. They can be dislodged during the first minute of de- 
velopment by holding a soft pad of absorbent cotton lightly against 

FIG. 8. Rack on unloading truck in drying 

the emulsion surface at one or two points near the upper shaft rollers ; 
or better, a soft rubber sponge of good quality cut to form a strip 
l 3 /s X 3 X */2 inch may be used. It is undesirable to have porous ma- 
terial such as this attached to the rack because of the danger of con- 
taminating the film or developer with hypo. 

Performance. Good uniformity of processing has been attained 
because of: (a) the high running speed of 150 feet a minute, (b) the 
strong agitation of the developer by compressed air, and (c) the use of 
an acid stop-bath. 

Acknowledgment. The assistance rendered by Mr. J. R. Turner 
and Mr. E. W. Jensen in working out several features in this new de- 
sign is gratefully acknowledged. 

404 C. E. IVES 


1 IVES, C. E. : "A Roller Developing Rack for Continuously Moving the 
Film During Processing by the Rack-and-Tank System," /. Soc. Mot. Pict. Eng., 
XXIV (March, 1935), No. 3, p. 261. 

2 WHITE, D. R. : "Equipment for Developing and Reading Sensitometric 
Tests," /. Soc. Mot. Pict. Eng. t XXVI (April, 1936), No. 4, p. 427. 

3 CRABTREE, J. I., AND IVES, C. E.: "A Pneumatic Film Squeegee," Trans. 
Soc. Mot. Pict. Eng., XI (Aug., 1927), No. 30, p. 270. 

4 CRABTREE, J. I., AND IVES, C. E.: "Rack Marks and Airbell Markings on 
Motion Picture Film," Trans. Soc. Mot. Pict. Eng., IX (Oct., 1925), No. 24, p. 95. 


During the Conventions of the Society, symposiums on new motion picture appara- 
tus are held in which various manufacturers of equipment describe and demonstrate 
their new products and developments. Some of this equipment is described in the 
following pages; the remainder will be published in subsequent issues of the Journal. 



Sound has been commercially recorded on 16-mm. film by a variety of methods, 
including direct recording on 16-mm. negative, re-recording from 35-mm. nega- 
tive to 16-mm. positive, and optical reduction from 35-mm. to 16-mm. Any of 
these methods that involve recording on 16-mm. film are subject to severe losses 
in frequency response due to the slit effect in recording. Batsel and Sachtleben 1 
show this loss to be approximately 12 db. at 5000 cps. for an 0.5-mil slit. 

Optical reduction prints may be made either by making an optically reduced 
negative from a 35-mm. positive and printing by contact, or directly from a 
35-mm. negative to a 16-mm. positive. The overall frequency response is nearly 
the same for either method, since the slight gain in contact-printing the 35-mm. 
positive offsets the 16-mm. contact-printing frequency losses. Contact printing 
tends to introduce the further difficulties of uneven slippage and poor contact, 
which adversely affect the sound quality. This consideration, together with the 
obvious advantage of economy of materials and time, indicates the desirability of 
making 16-mm. sound-track prints by direct optical reduction from the 35-mm. 

The present paper describes an optical reduction printer having several new 
features designed to facilitate operation and improve the quality of the finished 
sound-track. The printer departs from conventional design in that the film 
rolls, instead of being arranged in a vertical plane, are horizontal. This con- 
struction has resulted in considerable simplification in des : gn, and presents im- 
portant advantages in the operation of the printer. Oil-damped filters and flood- 
lubricated working parts are made possible without the use of friction-producing 
oil seals. There is no possibility of lubricating oil reaching any part of the film 
path. Several other advantages of the construction will be apparent from the 
following description. 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 18, 1938. 

** Bell & Howell Company, Chicago, 111. 




Fig. 1 shows the external appearance of the complete printer. The 16-mm. 
positive is at the top of the machine where it is readily accessible for threading. 
Each film roll rests upon a driving flange. The negative feed and take-up flanges 
are on the same spindles as the positive flanges. The covers A are placed over the 
negative film during printing to protect it from dust and other possible damage. 
Since the printer is designed to print alternately from beginning and end of the 

FIG. 1 View of complete printer. 

negative, and is arranged to stop at the end of the negative with the leader still 
threaded, it is necessary to have access to the negative only when changing 
negatives. A negative, once threaded, remains in the printer without further 
attention until the complete run of positives has been made. A pre-set stop 
mechanism stops the motor at the end of the negative and sets the reversing 

FIG. 2. Main drive assembly without motor. 

switches so that at the next starting the machine will operate in the reverse 

Fig. 2 shows the main drive assembly without the motor. The entire mecha- 
nism is driven from the main worm shaft, which is coupled to the motor by a 
safety clutch to protect the motor and working parts in case of jamming in the 
mechanism. The printer is reversed by reversing the 3-phase 220-volt syn- 
chronous motor. The printing speed is 60 feet of 35-mm. film per minute. All 

Oct., 1938J 



the driving gears are flood-lubricated by oil carrier gears which dip into the oil 
and carry it to the gear teeth. 

The flywheel is driven by the central worm, and the take-up spindles are driven 
by the two worm gears B. Unidirectional clutches are arranged so that the take- 

FIG. 3. 35-mm. sprocket. 

up spindle is driven and the feed spindle remains stationary. Hold-back and take- 
up tension is maintained by "arguto" washers upon which the film flanges rest, 
the weight of the film supplying the major part of the friction. This construction 
maintains very uniform film tension throughout the length of the film roll. 

Uniform film motion is the most important condition imposed upon an optical 
reduction printer. The excellence of the finished print depends entirely upon 

FIG. 4. Flywheel worm drive. 

driving the positive and negative films past the printing point at the proper rela- 
tive speeds, synchronized frame for frame, and without flutter or other improper 
motion. Synchronization requires that the two films be driven by positively con- 
nected sprockets. Uniformity of motion is attained most readily by means of a 
flywheel, carrying the films at the printing point on toothless drums. Shrinkage 



I6mm Film 

35mm Rim 

differences between positive and negative and variations in negative shrinkage 
make it impossible to connect the positive and negative film drums rigidly. Print- 
ers embodying various devices to reconcile these requirements have been described 
in the literature from time to time. 2 ' 3 - 4 

In the present printer, synchronism is achieved by mounting the sprockets in 
pairs, a 16-mm. and a 35-mm. sprocket to a pair, each pair on a common shaft. 
Each sprocket shaft is driven from the flywheel through helical gears. Slippage 
of the film over the root of the sprocket teeth is prevented by the two-piece con- 
struction of the sprockets (Fig. 3) . The film is supported by a cylinder slightly 
larger than the root-circle of the sprocket and free to rotate upon needle bearings 
on the sprocket itself, so that the film clears the root circle by approximately 1 

mil. This construction enables the 
film to move over the sprocket, as it 

G A /\| [Tj must to accommodate for shrinkage, 

yj without sliding contact, thus prevent- 

ing scratches. In addition, support- 
ing the film over its entire width 
reduces the strain on the edges of the 
film and prevents negative breakage. 

A massive flywheel and an oil drag 
drive are employed to insure exact uni- 
formity of motion of the film by a 
combination of "brute force" and vis- 
cous filtering. The large mass of the 
flywheel makes it impracticable to 
drive the flywheel by the film. In- 
stead, the driving motor drives the 
flywheel through the worm and gear 
shown in Fig. 4. Worm gear A is 
free to rotate upon the flywheel shaft 
which it drives through filter springs B. 
The natural period of oscillation of this 
assembly is sufficiently low effectively 
to prevent transmission of any possible 
motor or gear-tooth disturbances to the 
flywheel. Each printing drum is independently coupled to the flywheel by oil 
friction. This coupling consists of an interleaved set of thin plates, alternately 
connected to flywheel and film drum, and immersed in heavy oil. This cou- 
pling permits slow relative motion between the positive and negative films to 
accommodate for negative shrinkage. There will be a constant uniform relative 
motion between the two drums in direct proportion to the deviation of the actual 
negative shrinkage from the shrinkage for which the drums are designed. While 
permitting this necessary slow relative movement, the viscous coupling com- 
pletely eliminates any flutter or wow from sprocket teeth, splices, or film imper- 
fections by offering very high resistance to sudden movements. The area of 
contact and the film tension are sufficient effectively to prevent slipping of either 
film over its drum. 

Tension is maintained by spring-loaded idler rollers between the sprockets and 

FIG. 5. 


drums. Instantaneous response to film disturbance results from keeping the 
mass of the rollers as small as possible. Any disturbance is taken up by move- 
ments of these idlers and bending of the film without affecting the film drum ex- 
cept by a slow drift. 

Positive and negative films are guided by these rollers, the positive film on the 
edge and the negative by the perforations adjacent to the sound-track. 

The optical train is self-contained, and is removable as a complete unit by un- 
locking two clamping screws. All adjustments are made and the unit is sealed at 
the factory, making the optical units interchangeable and replaceable. The ways 
that locate the unit and the design of the clamping screws enable positive posi- 
tioning and focusing. 

Optical printing from 35-mm. to 16-mnt. requires the production on the 16-mm. 
film of an image of the 35-mm. track, moving in the same direction as the 16-mm. 
image and at the same speed, with a longitudinal magnification of 0.400 and a 
transverse magnification of 0.857. These requirements can be fulfilled only by 
a system containing cylindrical elements. In the present design, the proper 
direction of motion of the image is achieved without resorting to complicated erect- 
ing systems. Fig. 5 shows the optical layout. The negative is illuminated from 
inside the drum by lamp A, condenser B and prism C. An anastigmat lens D 
and a right-angled prism E form a full-size image of the moving 35-mm. track in 
the field lens F. Right-angled prism G and the two achromatic cylindrical com- 
ponents H, J form an image of this intermediate image in the 16-mm. film plane, 
with the proper magnification, moving in the proper direction. An area 0.063 X 
0.100 is scanned on the negative. Provision is made for printing two opaque 
lines along the edges of the track to cut down background noise and mask the 
edge of the printed area. 

The lamp is a photocell exciter lamp, 10-volt, 7.5 amperes, burned in a hori- 
zontal position in a water-cooled lamp house. The lamp is mounted in a special 
ring to assure accurate positioning of the filament. 

Lamp current is supplied by a pair of 6-volt storage batteries and a full-wave 
charger. The charger is set to charge at approximately 115 per cent of the 
normal lamp current, so that the lamp power is supplied by the charger with the 
batteries acting as ballast to remove the 120-cycle modulation in the charger 
current. This arrangement and the high thermal inertia of the lamp filament 
provide very constant illumination. Careful tests with an 0.5-mil slit showed 
complete absence of 120-cycle modulation. 

Lamp current is controlled by a pair of rheostats and an ammeter mounted in 
the control unit above the printing drums. 

A signal device is provided to make it possible to make any necessary changes 
in exposure during printing. Notches in the edge of the negative actuate a roller 
contactor which signals the change point. A standard card-rack is provided for 
timing cards. Safety switches automatically stop the motor should the negative 
break. The printer is intended to be operated in a darkroom, and is equipped 
with the necessary safelights for convenient operation. 


1 BATSEL, C. N., AND SACHTLEBEN, L. T.: "Some Characteristics of 16-Mm. 
Sound by Optical Reduction and Re-Recording," /. Soc. Mot. Pict. Eng., XXIV 
(Feb., 1935), No. 2, p. 95. 


2 SANDVIK, O., AND STREIFFERT, J. G.: "A Continuous Optical Reduction 
Sound Printer," /. Soc. Mot. Pict. Eng,, XXV (Aug., 1935), No. 2, p. 117. 

3 VICTOR, A. F.: "Continuous Optical Reduction Printing," /. Soc. Mot. 
Pict. Eng., XXIII (Aug., 1934), No. 2, p. 96. 

4 COLLINS, M. E.: "Optical Reduction Sound Printer," J. Soc. Mot. Pict 
En*., XXVH (July, 1936), No. 1, p. 105. 



The mechanism of the Model G Kodascope is completely housed in aluminum 
die castings, and is held to close tolerances both in parts and in assemblies (Figs. 1 
and 2). All shafts are ground to insure straightness, finish, and size. Diametei 
size is held within tolerances of =*= 0.0002 inch. All bearings are of the oilles? 
type, vacuum impregnated with oil shortly before assembly to give minimum weai 
over long periods of time. The teeth of the pull-down gears are cut after as- 
sembly to the shaft. Every assembly is checked for eccentricity, tooth spacing 
and finish; the allowable accumulative error in these assemblies is 0.0005 inch 
and further refinement is gained by the use of an adjustable sleeve for the bear 
ings of the pull-down shaft. The out side of the sleeve is eccentric with the 
bearing, so that each shaft may be adjusted for minimum backlash and correcl 
tooth mesh of the mating gears and then locked in position. The intermittenl 
movement consists of a tandem claw selectively hardened at points of wear, actu- 
ated by a Lumiere-type cam for the pull-down stroke, with a second cam govern- 
ing the in-and-out movement. The Lumiere cam and the pull-down claw are 
fitted together and kept in pairs during assembly. The periphery of the Lumiere 
cam is ground on a special grinder used only for this purpose, the overall distance 
across its face being held within a tolerance of 0.0003 inch measured at any point 
With this refinement and care in assembly, the operation of the mechanism i< 
exceptionally smooth and quiet. 

Threading is conventional and extremely easy. Sprocket frames open foi 
easy access to the sprockets, and the film slides into the gate. To facilitate this 
operation, the out position of the pull-down claw is designated by a milled side 
on the threading knob so that its position can be noted by touch as well as by 
sight (Fig. 3). 

Stills are shown by merely declutching the mechanism from the motor, al 
which time an automatic safety shutter swings into position to protect the film 
while the motor and fan continue to run for adequate lamp protection. By throw- 
ing a switch, the motor is reversed and pictures may be projected backwards 
Framing is accomplished by shifting the pull-down claw in relation to the aperture 
so that there is no movement of the picture on the screen. Sprockets, sprocket 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 18, 1938. 

** Eastman Kodak Co., Rochester, N. Y. 

Oct., 1938] 



guards, film-gate, aperture plate, and pull-down claw are all designed to operate 
sound-film without injury. 

Two features of the Model G deserve special mention. JThe first is the rewind. 
For rewinding, the movement of a single lever engages the rewind drive and re- 
leases the take-up reel. This lever is not only conveniently located for operation, 
but is so designed that it effectively obstructs the passage of film through the 
gate if left in the "rewind" position. 

FIG. 1. The Kodascope model G. 

Second, a single switch controls motor, threadlight, and projection lamp (Fig. 
i). This switch has four positions: in the first position, motor, threadlight, and 
amp are turned off; in the second position, the threadlight is turned on; in the 
:hird position, the motor is started and the threadlight remains on so that the 
operator can momentarily check his threading; and in the fourth position, the 
notor continues to run while the projection lamp is turned on and the thread- 



FIG. 2. 

The mechanism of the Koda- 
scope Model G. 

FIG. 3. 

Front view, showing threading knob and 
still picture control. 

Oct., 1938] 



light is turned off. A single knob adjacent to this switch controls the motor 
| speed. The threadlight is located at the side of the objective lens, and illuminates 
I the upper and lower sprocket and the gate so that no other light is needed for 
changing reels in a darkened room. 

The lamp house and the fan are 
designed to give adequate cooling for 
high-wattage lamps, insuring ample 
lamp life. The optical system was 
specially designed, and is remarkably 
efficient both as to picture quality and 
screen brilliance. 

Elevating or tilting either upward or 
I downward to center the picture upon 
he screen is accomplished by pivoting 
he mechanism on the pedestal base. 
This is controlled by an elevating 
mob which actuates a new elevating 
nechanism; it operates easily and 
iffords a fine adjustment. Similar to 
:he Model EE Kodascope, the base of 
.he Model G fits over the handle of 
:he carrying case, which may be used 
is a projection stand. 

A new 2-inch, //1. 6 lens, especially 
lesigned for flatness of field, is 
standard equipment. Other lenses 
nclude a 1-inch f/2.5 for short throws, 
md either a 3-inch //2.0 or a 4-inch f/2.5 for longer throws. These lenses, with 
he 400-, 500-, and 750-watt lamp's permit selection from twelve possible com- 
)inations. The standard model is fitted with arms for 400-ft. reels; however, a 
nodel for 1600-ft. reels will be available. The machine is finished in hand- 
ubbed glossy black lacquer, with all fittings in buffed chrome plate. 

FIG. 4. Unit control for thread- 
light, motor, and lamp. 



Up to now surgical filming has always been accompanied by sundry difficulties, 
vhich have often resulted in the decision not to film certain types of operations 
hat may not have been of paramount interest or the outcome of which could not 
>e predicted. This is easy to understand when one stops to consider all the com- 
)lications and preparations necessary before undertaking to film an operation, the 

* Received June 15, 1938. 
** Budapest, Hungary. 



many accessories and paraphernalia required in the operating room, and the tim 
taken to get everything ready for filming such feats. In the case of emergenc 
operations it has been nearly impossible to rig up the equipment in the short tim 
available, and it is fairly safe to say that the preparations for filming an operatic 
required at least half an hour before bringing in the patient. 

Some of the difficulties generally er 
countered are cited below; but, in ac 
dition, special problems arise in almos 
every case that have to be solved in th 
shortest possible time. 

It is obvious that the cameraman muj 
stand outside the sterile zone and wor 
in such a way as not to hinder th 
surgeon; in spite of which he nearl 
always wants extreme close-up shot; 
The lighting is perhaps the "trickiest 
problem. Everybody who has tried t 
take pictures of operations knows ver 
well how difficult it is to place the light 
in such positions as to provide reall 
uniform illumination over the area c 
interest; not interfere with the surgeor 
assistants, and nurses; and yet be suffi 
ciently removed from the sterile zone 
Nothing must be in the way of th 
light-beams that will cast shadows upo: 
the operation field and the rubber 
covered cables must be led along th 
walls so that no one may tread upo: 
them. To accomplish all this the light 
have usually been placed very higt 
necessitating the use of very high stands 
High stands of sufficient rigidity for us 
in operating rooms are not of the low 
priced variety. When the operation 
were performed within cavities, as withii 
the throat, ear, nose, teeth, and i] 
gynecological and other operations, th 
lighting offered generally such insur 
mountable difficulties that as a rule sue! 
regions were rarely if ever filmed. Ii 

these instances the light-source can be only a single unit, must be constructed s< 
as to provide a very narrow beam, and should be positioned as near the optica 
axis of the taking lens as possible. The ideal condition would be realized if thi 
beam could be made coincident with the optical axis. At the same time the bean 
must be able to follow, within certain limits, such pan or tilt movements of th< 
camera as may be necessary during the shooting. Since there is only a singL 
beam in such cases, it must be highly concentrated; but it must not be allowed t< 

FIG. 1. 

General view of surgical 
camera stand. 

Oct., 1938] 



cause excessive heating of the tissues and consequent discomfort of the patient in 
cases when no anesthetic is used. A very important matter is the possibility of 
making quick adjustments of the camera during the operation, so that the camera- 
man may avoid positions from which the surgeon would obstruct the view. The 
ability to change cameras is very useful when the reel runs empty during an in- 
teresting phase or when the camera is spring-driven rather than electrical. 

The difficulties outlined above have been eliminated effectively and by the 
surgical filming stand of original construction shown in Fig. 1. The stand is 
completely self-contained and once it is rolled into place the cameraman needs 
only to make the single connection to the 
current output and connect two rubber 
hoses to the water drain, which requires 
about ten minutes. 

The base is of heavy cast iron, to 
provide the necessary strength and elimi- 
nate all vibration even when working at 
high speeds for slow-motion effects. With 
minute adjustments at full lens opening 
it is important that the camera should 
not move because the depth of field is 
then very critical. Also, when shooting 
small areas (teeth, etc.) with the telephoto 
lens by using extension rings under the 
lens and thus working from great dis- 
tances, the slightest wabbling of the stand 
can easily spoil the macro-shot or even 
displace the camera sufficiently so as not 
to take in the required field. The total 
weight of the stand is about 50 kilograms. 
It moves on three rubber-covered rollers, 
and when in position is fixed by screwing 
three steel points down to the floor, thus 
obviating the slightest chance of wabble 
or vibration. The upright of the stand 
telescopes in two sections. One section 
provides the rough setting in height and 

the second (with a hand-wheel) is an accurate vernier adjustment. All adjust- 
ments can be fixed rigidly when in place. When raising or lowering the camera 
the lenses always point in the same direction. The lowest position of the tripod 
head is 85 cms., the highest 152 cms. above the ground. Thus every possible 
taking angle can be covered in minimum time. 

A special lamp house clamped to the lower part of the stand has been developed 
into a medical spotlight (Fig. 2). The lamp house is positioned vertically because 
[most projection lamps require a vertical filament position. The beam is directed 
through a condenser and concave mirror system to an internal plane mirror, 
j which throws the beam upward and through a second lens system which produces 
' the required directional spotlight effect. The lamp house is cooled by a revolving 
fan and the funnel-like middle piece has ample holes for ventilation. Under the 

FIG. 2. Lamp house attached 
to base of stand, showing cooling 
fan and hose connection for water 


top lens is a waterholder to cool down the beam although in practice this is not 
really necessary, except when photographing inflamed tissues. The water can 
circulate through the reservoir, entering by one rubber hose and leaving by the 
other. The lamp is a standard 250-watt projection bulb with two plane filaments, 
and provides ample light for all purposes, even for slow-motion shots at 64 frames 
per second on supersensitive reversal material at a distance of about 2 meters 
from the stand with a stop of f/2.8. 

The stand has a conventional pan and tilt tripod head for supporting the 
camera. A special device allows instantaneous attachment of the camera to the 
head by clamping, without screws, so that cameras may be changed in one second 
of time. Thus a loaded camera may be always held ready and put into place at 

FIG. 3. Detail of camera, showing plane mirror for di- 
recting light on operation field. 

the moment the one on the stand runs empty. There is always time, however, 
to rewind the taking camera upon the stand between phases of the operation. 
An electrical drive may, of course, be provided to permit shooting the full length 
of the 100-ft. reel, when required, without rewinding; but in practice this has 
never been found to be necessary, the 18-ft. run of the spring-drive having always 
been adequate. A wire release operated by means of a pedal allows the surgeon 
to make shots himself during an examination or an easy operation. Of course, 
he must have an assistant in any event. 

The beam of the spot is directed to the operating field by a plane mirror fixed 
to the pan and tilt head (Fig. 3). This mirror can be moved and clamped in any 
desired direction by the universal ball-joint on its back. The area illuminated is 
checked in the view-finder, and the beam can be made fairly close to the optical 
axis of the lens, giving the best illumination for every purpose and the most ex- 


cellent results when photographing cavities. Furthermore, as the mirror moves 
together with the camera when tilting or panning within reasonable limits (such 
as occur in work of this sort) the beam always follows th& direction of the lens and 
illuminates the photographed area in all cases. The divergence of the beam has 
been calculated to have an angle of divergence of approximately 30 degrees so as 
to cover the field to its borders even with relatively generous angles of tilt and 

A Paillard Bolex 16-mm. camera was used, equipped with a special eyepiece for 
controlling the focus from the back. Also extension rings were used under the 
telephoto lens to make macro-shots from relatively great distances. The inside 
of the throat of a dog, for instance, filled the whole screen. The shot was made 
using an extension ring with a telephoto lens of 75-mm. focus from a distance of 
1.5 meters. 

As an example of the splendid results attained with this stand may be men- 
tioned a slow-motion shot of vibrating vocal chords taken in the living throat 
Of course, the spotlight may be put out of use if not needed; for simple surgical 
shots two horizontal rod-holds are provided for two regular photoflood bulbs in 
standard reflectors on both sides of the camera. It is believed that cameramen 
using this stand for surgical shots will greatly enjoy the extraordinary facilities 
that its use makes possible. 



The editors present for convenient reference a list of articles dealing with subjects 
cognate to motion picture engineering published in a number of selected journals. 
Photostatic copies may be obtained from the Library of Congress, Washington, D. C., 
or from the New York Public Library, New York, N. Y. Micro copies of articles 
in magazines that are available may be obtained from the Bibliofilm Service, Depart- 
ment of Agriculture, Washington, D, C. 

Journal of the Acoustical Society of America 

10 (July, 1938), No. 1 
On Distortion in Sound Reproduction from Phonograph 

Records (pp. 14-28). 
Finite Solid Acoustic Filters (pp. 41-44). 

Acoustical Output of Air Sound Senders (pp. 50-62). 







American Cinematographer 

19 (July, 1938), No. 7 
Just One Camera Problem after Another Created by 

Speedy Sonja (pp. 268-9, 271). J. J. MESCALL 

Dr. Carter Outlines History of Search for Permanent 

Photograph (pp. 270-1). R. W. CARTER 

Journal of the British Kinematograph Society 

1 (May, 1938), No. 2 
Screen Brightness and its Measurement (pp. 68-89). 

The Structure of the Industry (pp. 90-98). 

A Precision Instrument for the Determination of Expo- 
sure (pp. 99-119). 

Photographic Technique for Variable-Area Recording 
(pp. 120-36). 

A Brief Description of the British Realita Process (pp. 


18 (July, 1938), No. 7 

Notes on New Television Standards (pp. 5-8, 34). 
Standard Speech-Input Assemblies (pp. 15-18, 24, 29- 

An Impedance Meter (pp. 23-4). 









11 (July, 1938), No. 7 

A Laboratory Television Receiver (pp. 16-20). 
Volume Indicator- Attenuator (pp. 22-4). 
A New Television Film Projector (p. 25). 


RMA Completes Television Standards (pp. 28-9, 55). A. F. MURRAY 

International Photographer 

10 (July, 1938), No. 6 
News of New Products (pp. 1-7). 

Protize Process (pp. 9-10). S. P. SOLOW 

Grip Equipment (pp. 14, 16). G. M. HAINES 

Analysis of Developing Solutions (p. 22). D. K. ALLISON 

SMPE Theater Survey Report (pp. 24-7). 

International Projectionist 

13 (June, 1938), No. 6 
Take-Up Troubles: How to Locate and Correct Them 

(pp. 7-8, 34). A. C. SCHROEDER 

Sound Equipment Troubles: Hum (pp. 11-12, 14). A. NADELL 

MGM Film Lubrication Policy (p. 14). J. M. NICKOLAUS 

Academy Research Council Nomenclature for Release- 
Print Sound-Tracks (pp. 22-24). J. K. HILLIARD 

13 (July, 1938), No. 7 

Some Common Sources of Noise in Theater Sound Sys- 
tems (pp. 7-8, 11, 13). A. NADELL 

Academy Recommendations on Theater Sound Repro- 
ducing Equipment (pp. 14-15, 29, 30). 

Take-Up Troubles : How to locate and Correct Them 

(pp. 17-19). A. C. SCHROEDER 

Kinematograph Weekly 

257 (July, 1938), No. 1629 

New Apparatus from Vinten Workshops: Gamma 
Gauge, Negative Grader, and a High-Speed Camera 

(P. 33). 


20 (July, 1938), No. 7 

Wiedergabe tiefer Tone hoher Leistung. (High-Fre- 
quency Reproduction) (pp. 172-3). 

Die Kinotechnik in der Lehrschau der Ufa (Ufa Educa- 
tional Exhibit) (pp. 174-6). 

Eine neue Kleinapparatur fur Tonfilmaufnahme (New 
Small Sound Recording Camera) (pp. 176-9). 

Konstruktion von Schmalfilmprojektoren nach licht- 
technischen Grundsatzen (Contruction of Substand- 
ard Projectors on the Principles of Light Optics) (pp. 







Allgemeine raumakustische Betrachtungen zur elektro- 
akustischen Schallaufnahme (General Observations 
on Room Acoustics for Electrical Recording) (pp. 

Die Messung des photographischen Gleichrichteref- 
fektes (Measurement of Photographic Rectifying Ef- 
fect) (p. 187). 

Neue Umkehr-Emulsionen fur Schmalfilm (New 
versal Emulsions for Substandard Film) (p. 193). 


Journal of the Optical Society of America 

28 (July, 1938), No. 7 

An Experimental Study of Latent-Image Formation by 
Means of Interrupted and Herschel Exposures at Low 
Temperatures (pp. 249-63). 

Philips Technical Review 

3 (Apr., 1938), No. 4 

The Behavior of Amplifier Valves at Very High Fre- 
quencies (pp. 13-11). 

Photographische Industrie 

36 (July 6, 1938), No. 27 

Filmpflege, ihre physikalischen und chemischen Beding- 
ungen. I. (Physical and Chemical Limitations in 
the Care of Film. I) (pp. 783-6). 

36 (July 13, 1938), No. 28 

Filmpflege, ihre physikalischen und chemischen Beding- 
ungen. II. (Physical and Chemical Limitations in 
the Care of Film. II) (pp. 807-10). 


W. Vox 









Officers and Committees in Charge 

W. C. KUNZMANN, Convention Vice-President 
J. I. CRABTRBB, Editorial Vice-President 
G. E. MATTHEWS, Chairman, Papers Committee 
H. GRIFFIN, Chairman, Projection Committee 
E. R. GEIB, Chairman, Membership Committee 
J. HABER, Chairman, Publicity Committee 




Local Arrangements 

K. BRBNKERT, Chairman 




Registration and Information 

W. C. KUNZMANN, Chairman 



Hotel and Transportation Committee 

A. J. BRADFORD, Chairman 






H. GRIFFIN, Chairman 





Officers and Members of Detroit Projectionists Local No. 199 



J. F. STRICKLER, Chairman 



422 FALL CONVENTION [j. s. M. P. E. 


J. HABER, Chairman 



Ladies' Reception Committee 

MRS. J. F. STRICKLER, Hostess 

assisted by 





The Headquarters of the Convention will be at the Hotel Statler, where excellent 
accommodations are assured. A reception suite will be provided for the Ladies' 
Committee, who are now engaged in preparing an excellent program of entertain- 
ment for the ladies attending the Convention. 

Special hotel rates guaranteed to SMPE delegates and friends, European plan, 
will be as follows : 

One person, room and bath $3.00 to $6.00 

Two persons, room and bath 5.00 to 8.00 

Two persons (twin beds), room and bath 5.50 to 9.00 

Three persons, room and bath 7.50 to 10.50 

Parlor suite and bath, for one 8.50 to 11.00 

Parlor suite and bath, for two 12.00 to 14.00 

Room reservation cards will be mailed to the membership of the Society in the 
near future, and everyone who plans to attend the Convention should return his 
card to the Hotel promptly in order to be assured of satisfactory accommodations. 
Registrations will be made in the order in which the cards are received. Local 
railroad ticket agents should be consulted as regards train schedules, and rates to 
Detroit and return. 

The following special rates have been arranged for SMPE delegates who motor 
to the Convention, at the National-Detroit Fireproof Garage (the Hotel Statler's 
official garage), Clifford and Elizabeth Streets, Detroit: Self -delivery and pick-up, 
12 hours, $0.60; 24 hours, $1.00; Hotel-delivery and pick-up, 24 hours, $1.25. 
Special weekly rates will be available. 

Technical Sessions 

An attractive and interesting program of technical papers and presentations is 
being assembled by the Papers Committee. All technical sessions, apparatus 
symposiums, and film programs will be held in the Large Banquet Room of the 

Registration and Information 

Registration headquarters will be located at the entrance of the Large Banquet 
Room, where members of the Society and guests are expected to register and re- 
ceive their badges and identification cards for admittance to the sessions and film 

Oct., 1938] FALL CONVENTION 423 

programs. These cards will be honored also at the Fox Detroit Theater, through 
the courtesy of Mr. David Idzol, and special passes will be furnished to registered 
members and guests for admittance to the Michigan United Artists and Palms- 
State Theaters, through the courtesy of the United Detroit Theaters Corporation. 

Informal Luncheon and Semi-Annual Banquet 

The usual Informal Luncheon will be held at noon of the opening day of the 
Convention, October 31st, in the Michigan Room of the Hotel. On the evening of 
Tuesday, November 1st, the Semi-Annual Banquet of the Society will be held 
in the Grand Ballroom of the Hotel at 8 P.M. Addresses will be delivered by 
prominent members of the industry, followed by dancing and other entertainment. 

Tours and Points of Interest 

In view of the fact that this Convention will be limited to three days, no 
recreational program or tours have been arranged. However, arrangements 
may be made for visits to the Jam Handy plant and to other points of technical 
and general interest in Detroit on the day following the Convention, namely, 
November 3rd. Arrangeir ents for such trips may be made at the registration 
headquarters of the Convention. 

In addition to being a great industrial center, Detroit is also well known for the 
beauty of its parkways and buildings, and its many artistic and cultural activities. 
Among the important buildings that one may well visit are the Detroit Institute 
of Arts; the Detroit Historical Society Museum; the Russell A. Alger House, a 
branch of the Detroit Institute of Arts; the Cranbrook Institutions; the Shrine 
of the Little Flower; and the Penobscot Building. 

At Greenfield Village, Dearborn, are grouped hundreds of interesting relics of 
early American life, and there also is located the Edison Institute, established by 
Henry Ford in memory of Thomas A. Edison. 

On the way to Greenfield Village is the Ford Rotunda, a reception hall for visi- 
tors to the Ford Rouge Plant. Here are complete reproductions and displays of 
motorcar design, and representations of the famous highways of the world, from 
Roman days to modern, are on the grounds surrounding the building. 

The General Motors Research Building and Laboratory, located on Milwaukee 
Avenue, will be of particular interest to engineers visiting the City. 

Various trips may be taken from Detroit as a center to Canada, by either the 
Ambassador Bridge or the Fleetway Tunnel; to Bloomfield Hills, a region of 
lakes; Canadian Lake Erie trip from Windsor, Ontario; to Flint, Michigan, 
another center of the automotive industry; to Milford, General Motors' Proving 
Grounds; and to the Thumb of Michigan Resort Beaches. The City contains 
also a number of beautiful parks and golf courses. 



DETROIT, MICH., OCT. 3i-NOV. 2, 1938 

The Papers Committee submits for the consideration of the membership the follow- 
ing abstracts of papers to be presented at the Fall Convention. It is hoped that the 
publication of these abstracts will encourage attendance at the meeting and facilitate 
discussion. The papers presented at Conventions constitute the bulk of the material 
published in the Journal. The abstracts may therefore be used as convenient refer- 
ence until the papers are published. 

G. E. MATTHEWS, Chairman 
L. A. AICHOLTZ, Chairman, West Coast 







" Some of the Problems Ahead in Television"; I. J. Kaar, General Electric Co. 
Bridgeport, Conn. 

Now that television standards have been agreed upon in the United States, 
commercial receiving sets will undoubtedly be available very soon, and regularly 
scheduled television programs may be expected at the same time. How good 
will the television be and what are the problems yet to be solved before television 
reaches the technical maturity that radio has today? These are questions of con- 
siderable interest to engineers in related fields, and are the subject matter of the 
present paper. The quality of present-day television pictures is compared with 
that of motion pictures both in the theater and in the home. A discussion is given 
of the problems that have been solved to make television what it is today, and con- 
sideration is given to the problems that must be solved to make television what we 
hope it will be tomorrow. The problems of signal propagation and interference 
are discussed, and the matter of network program distribution is considered. 
Finally, a short introduction is given to the commercial problems in television. 

"Some Production Aspects of Binaural Recording for Sound Motion Pictures"; 
W. H. Offenhauser, Jr., New York, N. Y., and J. J. Israel, Brooklyn, N. Y. 

Binaural sound recording for motion pictures has a long development history of 
worthy achievement, yet to date it has not found application in our everyday en- 
tertainment sound motion picture. Inspection of the situation reveals that, like 



stereoscopic pictures, there is not complete acceptance of any of the various theo- 
ries and that the shades of interpretation are so many that it is difficult to secure 
a consensus on what constitutes binaural sound recording for motion pictures. 
Instances are cited to show that "theoretically perfect "*sound is not necessarily 
the objective ; in fact, since it is the illusion produced, both by sound and picture 
that is in the final analysis important, "theoretically perfect" sound may even de- 
stroy the illusion we are trying to create. 

The history of binaural sound recording for motion pictures is reviewed and 
especial reference is made to the early developments of Rosenberg and Kuechen- 
meister. A short review of the developments since the work of these pioneers 
covers in a general way the advance of the binaural sound motion picture recording 
art to date. The production requirements of binaural sound recording for 
motion pictures are analyzed briefly and the importance of the editing process in 
the production of the finished picture is outlined. 

A new binaural sound motion picture production technic is suggested, based upon 
the developments of the authors, that may be quite readily adapted to present- 
day monaural production technic. It is pointed out that the perspective sound 
control, which is an important added feature, does not affect shooting stage op- 
erations; this control is suggested as a logical part of dubbing-room operations. 
Some of the effects produced include variation of apparent recording-room size 
from very small, say, 1000 cu. ft. to very large, say, 500,000 cu. ft. Another 
important effect is the simultaneous yet essentially independent movement of one 
sound-source with respect to another and the essentially independent left-right 
movement. All these effects are possible wi+h no movement whatever of the 
sound-source or sources with respect to the microphones. Essentially the same 
effects can be obtained with the pseudo-binaural system, a system in which it is 
possible to take a completed picture of the conventional monaural type and by a 
simple dubbing operation, provide practically all the important binaural charac- 
teristics without any additional original sound recording whatever. The effects 
described will be demonstrated. 

"The Spectraheliokinematograph"; R. R. McMath, McMath-Hulbert Ob- 
servatory, University of Michigan, Ann Arbor, Mich. 

Taking motion pictures of celestial phenomena that show change is not as 
simple as it would appear at first thought. This work was started in 1928, and 
in 1931 the instrumentation was donated by the founders of the McMath-Hulbert 
Observatory to The University of Michigan. 

The combined tower telescope and spectroheliokinematograph of the McMath- 
Hulbert Observatory at Lake Angelus, Mich., is now one of the most powerful 
pieces of solar apparatus in the world. The optical train will be explained by 
means of slides, and then the apparatus itself will be illustrated by motion pic- 
tures. A second reel will show solar prominences in motion. 

"Underwater Cinematography"; E. R. F. Johnson, Mechanical Improvements 
Corp., Moorestown, N. J. 

The dates of the first recorded use of underwater photography and the tenden- 
cies toward its increasing use by producers are noted. The author's early ex- 
periences in this field are described. The opinion is expressed that for work in 
natural settings the most useful equipment consists of submergeable cameras 

426 FALL CONVENTION [j. s. M. P. E. 

placed on the bottom and operated by divers. The rest of the paper deals with 
the problems of and equipment for such work. It is pointed out that studio 
tank work shares most of these problems. 

The optical properties of water are described. Since water is less transparent 
than air, photography by natural light is limited to small depths and more power 
is required for artificial illumination under water. Since colors are not absorbed 
equally, accurate monochrome rendering and photography in natural color 
are complicated. Water haze limits the distance at which pictures can be taken 
under water. This haze is largely confined to a part of the spectrum and can be 
eliminated partially by color-filters. It is polarized and can therefore be elimi- 
nated also by polarizing plates. The advantages of this method are briefly 
stated: they do not distort the monochrome rendering, and may be used in natu- 
ral-color photography. The ideal attributes of equipment for use in under- 
water cinematography are outlined and available equipment is briefly described. 

"Improving the Fidelity of Disk Records for Direct Playback"; H. J. Has- 
brouck, RCA Manufacturing Co., Inc., Camden, N. J. 

Recent advances in equipment design and in materials of which recording disks 
are composed, have resulted in improved fidelity. Both the volume range and 
the frequency range have been extended, satisfying present-day requirements of 
motion picture and broadcast applications. 

For reproduction, there is provided a new lighter weight lateral pick-up having 
high sensitivity and equipped with a permanent diamond point. This reproducer, 
in combination with its associated circuit, is suitable for use on all laterial-cut 
disk records. 

Pre- and post-equalization are employed in the method described for making 
high-fidelity records, insuring an extremely low noise-level. This absence of 
background noise together with the wide frequency range and low overall dis- 
tortion create an illusion of reality or "presence" during reproduction. 

Usually a great many playings are not required of direct playback disks. 
However, because of the low mechanical impedance of the new RCA pick-up and 
the improved composition of the disks it is possible to reproduce 75 to 100 times 
without appreciable increase in noise or distortion. Great differences in record 
life under various conditions of handling have been noted and are attributed 
chiefly to accumulation of fingerprints and dust on the record surface. Gradual 
oxidation of the lacquer coating must also be considered and guarded against by 
special care when records of this type are intended for long preservation. 

"Characteristics of Film-Reproducing Systems"; F. Durst, International Pro- 
jector Corp., New York, N. Y. 

An analysis of sound-picture reproducing-system characteristics, including 
electrical and acoustical response data collected in the interest of determining the 
possibilities involved in obtaining an average characteristic for reproducing vari- 
ous film products with uniform response over several combinations of loud speaker 
equipment. With the aid of a curve tracer having a long-persistent cathode-ray 
screen, a photographic record was made of the characteristics, starting with 
various forms and amounts of equalization and exploring their relationship to the 
power-handling capacity of amplifiers. Following through the system, this 
record shows the characteristics of dividing networks under various conditions of 

Oct., 1938] FALL CONVENTION 427 

load, and finally the acoustical response curves taken for comparison of the loud 
speaker equipments under study. 

The measurements of loud speaker combinations included various types of 
units, both permanent-magnet and energized, low-frequency horns ranging from 
open back baffles to folded horns with specially designed rear-loading compart- 
ment, and high-frequency multicellular horns of various configurations and con- 
structional details. 

After establishing the natural characteristics of the various equipments in- 
volved, careful listening tests were made over an extended period with samples of 
commercial prints and other recordings. A description follows of the difficulties 
and problems involved in an effort to obtain one overall characteristic, which 
would give satisfactory reproduction for all types of material. The final results 
are shown, with a short discussion of the methods for duplication in other equip- 
ment combinations, and conclude with recommendations for future designs and 

"Some Practical Accessories for Motion Picture Recording"; R. O. Strock, 
Eastern Service Studios, Long Island City, N. Y. 

The addition of practical operational accessories to standard recording chan- 
nels as purchased expedites operation and saves time. At the Eastern Service 
Studios a number of such accessories have been designed and will be described 
briefly. It is the purpose of this paper to show what has been done at one studio 
in the hope that it may be of some interest and help to others who are engaged in 
recording work. 

Included in the equipment are the following items : A small collapsible, portable 
microphone boom for location work; a special microphone suspension to pre- 
vent mechanical noises from getting into the recording system; a small mixer 
console for stage work, to permit the mixerman to operate close to the scene of 
action; an accurate illumination meter, using a microammeter, for setting and 
checking the recording machine exposure; a compact re-recording mixer console 
equipped with equalizers, effect filters, amplifiers, and attenuators; a projected 
volume indicator and footage counter for use in re-recording rooms; a film play- 
back adapter for use on a Western Electric film machine for location use; play- 
back horns for stage and location use; and an air-brush adaptation for blooping 
re-recording tracks. 

"The Lighting of Theater Interiors"; F. M. Falge, General Electric Company, 
Cleveland, Ohio. 

Here and there a theater is planned with lighting features utilizing the funda- 
mental principles that have been expounded on many occasions. In too many 
cases, however, interior lighting has lagged far behind exterior lighting for ad- 
vertising, and owner and public alike have suffered. In too many cases, also, 
the theater falls far short of complementing the attractive scenes so well pro- 
jected upon the screen. 

This paper reiterates the aims and advantages of proper lighting, and outlines 
the problem of locating, coloring, and controlling the lighting properly so that it 
will be comfortable and pleasing and an aid, psychologically. It discusses the 
possibilities of systems of lighting such as downlighting and fluorescent lighting. 
New materials and new light-sources will be demonstrated and discussed. 

428 FALL CONVENTION [j. s. M. p. E 

New equipment for brightness measurement will also be shown as an aid 11 
building up a quantitative background of what conditions conduce to comfor 
and satisfaction. 

"The Evolution of Arc Broadside Lighting Equipment"; P. Mole, Mole-Rich 
ardson Co., Hollywood, Calif. 

From the earliest days of artificial lighting of motion picture sets the broad 
side type of unit has been a fundamental lighting tool. Regardless of the typ 
of light-source used in such lamps whether mercury-vapor tubes, carbon arcs, o 
incandescent filament globes the broadside is a lamp of the floodlight type, de 
signed to emit a relatively wide flood of soft, moderately powerful illumination 
It has withstood innumerable sweeping changes in lighting and photograph! 
technic, including the introduction and acceptance of spotlighting, the chang 
from orthochromatic to panchromatic film materials, the changes from silent fc 
talking pictures and from arc to incandescent light-sources, and the present grow 
ing popularity of natural-color photography. 

The present paper will trace the evolution of arc broadsides only. It will com 
ment upon the design and performance of the early-day units, which were adapte< 
almost intact from previous similar lamps used in photoengraving. It will follow 
the evolution of the broadside through successive improvements in silent-pictur 
usages; through its decline at the introduction of sound and Mazda lighting 
through the relatively recent rebirth of arc lighting due to the requirements o 
modern natural-color photography; and the most recently introduced units o 
this type which are replacing equipment designed less than five years ago at th 
introduction of the three-color Technicolor process. Comparison will be mad* 
between the early, intermediate, and modern units as regards color distribution 
light distribution, steadiness and length of burning period, indicating that thougl 
less public attention has been given to these types than to the more familiar spot 
lighting units, the broadside has kept pace with advances in lighting and equip 
ment design. 

Report of the Projection Practice Committee; H. Rubin, Chairman. 

This report deals with two major projects completed by the Committee withh 
the past six months, namely, the third revision of the Projection Room Plans anc 
the proposed revision of the NFPA "Regulations for Handling Nitrocellulose 
Motion Picture Film." These two projects are given in detail. Other project: 
now under consideration by the Committee are briefly mentioned. 

"A Machine for Artificial Reverberation"; S. K. Wolf, Acoustic Consultants 
Inc., New York, N. Y. 

Sometimes there arises the necessity of introducing into recorded sound a live 
ness that is not present in the original sound-waves impinging upon the micro 
phones in the recording studio. Reverberation chambers have been used to pro 
vide the additional liveness, but such chambers are not very flexible in use and an 
costly to install. 

A new machine has been developed by means of which reverberation may b< 
introduced into the recorded sound artificially. The sound is recorded upon ai 
endless magnetic sound-carrier or tape, which passes beneath a number of pick 
ups or reproducers at intervals along the carrier. These pick-ups are connectec 
to a mixer panel, and the sound level of each is adjusted to produce the reverber 

Oct., 1938] FALL CONVENTION 429 

ant effect required. After passing the last pick-up head in the series, the sound 
is "wiped off" the magnetic carrier. 

Such a machine finds many applications, and is useful not only in studios for 
direct recording, but also for adding liveness to records during the process of 

"A Silent Wind Machine for the Production Stage"; F. G. Albin, United Art- 
ists Studio Corp., Hollywood, Calif. 

The machines generally used on the motion picture production set to create 
wind for pictorial effects are large motor-driven propeller fans mounted on floor 
stands. The noise level produced at high velocities is so high that satisfactory 
sound recording of the scene is practically impossible. Furthermore, the size and 
shape of these machines are such that they must be placed at such a distance that 
the directivity is not readily controllable. The additional hazard to sound re- 
cording of causing wind around the microphone always exists and, commonly, the 
desirable microphone placement is sacrificed in order to avoid the wind. 

A new type of wind machine has been adopted and used for several years with a 
great improvement realized. The new type is a centrifugal blower, such as is 
commonly used in ventilating systems. The air is conducted by means of light 
canvas ducts from the exhaust of the blower to the set where the scene is being 
enacted. The ducts are equipped with variously shaped fittings and nozzles so 
that the air stream may be directed as desired. 

It has been found expedient to locate the blower outside the stage building and 
enter the duct through a special portal. Thereby, the greatest noise source, the 
blower, is remotely located and insulated from the scene by the walls of the stage 
building. Furthermore, it incidentally serves as a ventilator, supplying fresh air 
to the scene. Measurements of noise level for various wind velocities indicate 
improvements up to 70 decibels in noise reduction. Thus sound recordings of 
scenes requiring wind are made possible where heretofore it was necessary to 
photograph the scene without sound and provide synchronized sound subse- 

"Silent Variable-Speed Treadmill"; J. E. Robbins, Paramount Pictures, Inc., 
Hollywood, Calif. 

Treadmills of various designs have been used by the motion picture industry 
for many years for obtaining animated shots in front of moving backgrounds. 
The adoption of sound practically eliminated them except for synchronized and 
other types of silent scenes. 

This loss was keenly felt, and as a result immediate steps were taken to develop 
a unit that could operate throughout a wide range of speed, with fine control, 
instantaneous start and stop, and ability to reverse in the same shot, still main- 
taining a noise level that would allow the recording of intimate, quiet dialog. 
This was not as simple as it appeared, due to the fact that in addition to the 
above-mentioned requirements it also had to support the weight of two horses 
running, fifteen or twenty men on a inarch, automobiles and motorcycles in mo- 
tion, etc. This all had to be accomplished with a unit restricted in size and 
weight in order to maintain mobility. 

The paper discusses the problems confronting the engineering and mechanical 
departments throughout the design and construction of a machine that comes 
fairly close to doing all that was hoped for originally. 

430 FALL CONVENTION [j. s. M. P. E. 

"Independent Drive for Camera in the A-c. Interlock Motor System"; F. G. 
Albin, United Artists Studio Corp., Hollywood, Calif. 

The "Selsyn" or alternating-current interlock motor system used to drive 
cameras, recording, re-recording, and projection machines in synchronism, is a 
popular type of motor system in large studios. It has special advantages in such 
applications as driving projector and camera for projection background process. 
The one inexpedient feature is that the system is generally started from a central 
point such as the recording room, and the cameraman does not have means for 
running his camera independently as is so often required for photographing slates, 
exposure tests, and silent scenes. 

An addition has been made to the a-c. interlock system to give it the advantages 
possessed by the synchronous motor system: namely, the facilities enabling the 
cameraman to operate his camera at will at regular speed . 

The addition consists of a set of relays with control circuits, and a frequency 
changer and field exciter set. Normally, the camera motors are connected to the 
common interlock system through the relays. If, however, the button provided 
at the camera is depressed, the pilot relay operates and energizes the main relays 
which transfer the camera motor circuit to the bus of the frequency changer and 
field exciter set. The camera motor is operated as a true synchronous motor. 
One phase of the rotor is short-circuited, and the remainder is excited with direct 
current and serves as the field. The three-phase stator is supplied with three- 
phase power of a frequency that will cause the motor to run at the required speed, 
the same speed as when driven with the interlock system. 

The power developed by the a-c. interlock camera motor when operated as a 
synchronous motor is approximately the same as under normal operating condi- 
tions. The acceleration is typical of small synchronous motors when the power 
supply is suddenly connected. The pull-in torque is superior to the slotted-rotor 
type of as-synchronous motor. The operation of the system is smooth, simple, 
and efficient, and has, after several years of use. proved its value. 

"A 16-Mm. Studio Recorder"; R. W. Benfer, Electrical Research Products, 
Inc., New York, N. Y. 

Recent advances in the commercial use of 16-mm. sound-film have stressed the 
importance of improving the product. Certain limitations imposed by the optical 
reduction process for obtaining 16-mm. sound prints are eliminated by recording 
16-mm. negatives expressly for contact printing. A studio recorder for this pur- 
pose is described. The paper deals briefly with the results of considerable investi- 
gation to determine the desirable recording characteristics and concludes with a 
demonstration of experimental recordings. 

"New Sound Recording Equipment"; D. R. Canady and V. A. Welman, Can- 
ady Sound Appliance Co., Cleveland, Ohio. 

Recorder for 16-Mm. Film. This recorder is characterized by its constancy of 
speed and its convenience and simplicity of operation. The constant-speed drum 
is not affected by temperature changes. The recorder has an aluminum magazine 
of 400-ft. capacity, with friction take-up and fitted for either galvanometer or 
glow-lamp recording, the glow lamp being preferred because of its simplicity. 

Noise- Reduction Unit for Glow-Lamp Recording. A self-contained unit, either 
portable or for panel mounting, which provides polarizing voltage and noise 

Oct., 1938] FALL CONVENTION 431 

reduction for glow-lamp recording. It has simple adjustments for setting the 
minimum and maximum current desired, and when these adjustments are set the 
unit is fully automatic. It is variable over a wide range and will give recordings 
from 5 to 25 ma. of current or from nearly clear negative to fully exposed negative. 
It has no time lag, can not react in any way with the amplifier, and may be con- 
nected to any amplifier. 

Galvanometer for 35- or 16-Mm. Recording. An oil-damped galvanometer, so 
designed that each of its component parts is readily adjustable, making it possible 
to be fitted to almost any recorder. The galvanometer has a straight-line output 
to 10,000 cycles. 

Projector for Background Projection. A claw projector, noiseless in operation 
and rock-steady, designed for the extreme requirements of background projection. 
The claws have three teeth on each side, the tension shoes are long, with adjustable 
tension, and the wear on the film is a minimum. The mechanical parts are en- 
closed and lubricated by an oil pump from an oil sump. 

"A Color-Temperature Meter"; E. M. Lowry, Kodak Research Laboratories, 
Rochester, N. Y. 

The recent advances in color photography have made more apparent than ever 
before the need for some simple and accurate method for the estimation of the 
color-temperature of light-sources. Photographers, whether professional or 
amateur, are only too well aware of the influence that the quality of the illu- 
mination has upon the color rendering of photographic subjects. For example, 
the difference in color-temperature between general-purpose tungsten filament 
lamps, and studio modeling lamps, or between modeling lamps and photoflood 
lamps, is often the deciding factor between correct and incorrect photographic 
color reproduction. In order that the photographer may easily determine the 
quality of the lighting he is using and make the proper adjustments to secure 
standard lighting conditions, an instrument that is at once compact, simple in 
operation, and accurate, has been developed in these laboratories. No auxiliary 
light-source is required for making measurements since each source is tested by 
means of the radiant energy that it itself emits. In this paper a discussion of 
the principles applied in construction of the instrument, a description of the 
instrument, and data showing the probable error of results are given. 

"Some General Characteristics of Chromium-Nickel-Iron Alloys as Corrosion- 
Resisting Materials"; R. Franks, Union Carbide and Carbon Co., Inc., Niagara 
Falls, N. Y., and F. L. LaQue, International Nickel Co., Inc., New York, N. Y. 

Those features of the chromium-nickel stainless steels are described that make 
these alloys useful as corrosion-resisting materials, and data are presented on the 
influence of the several alloying elements commonly present. It is shown how 
the high chemical activity of chromium benefits corrosion-resistance by reaction 
with oxygen or other oxidizing agents to form inert films which prevent progres- 
sive attack. The effect of chromium content upon corrosion resistance in 
typical reducing and oxidizing solutions is illustrated by test data. 

Data are presented to illustrate the effect of nickel in achieving the desirable 
austenitic state, in increasing the stability of the alloys, and in supplementing 
the protective film-forming properties of chromium. Included in the discussion 
are iron-base alloys with chromium predominating, iron-base alloys with nickel 

432 FALL CONVENTION [j. s. M. P. E. 

predoirinating, and nickel-base alloys containing high percentages of chromium. 
The peculiar usefulness of each type of alloy is indicated and illustrated with 
appropriate data. 

The effect of molybdenum is treated in much the same way as the effect of 
nickel. The usefulness of molybdenum in improving corrosion resistance under 
both oxidizing and reducing conditions is pointed out, as well as its specific 
beneficial effects in connection with organic acids and vapors, and in reducing 
the susceptibility to local attack or pitting by chlorides or other halogen com- 

There is included, also, a discussion of the effects of carbon upon corrosion- 
resistance with especial reference to intergranular corrosion of the austenitic 
alloys. Supplementing this discussion of carbon there is a description of several 
methods of avoiding intergranular corrosion, including the use of such stabilizing 
elements as columbium and titanium. 

" Coordinating the Acoustical and Architectural Design of the Motion Picture 
Theater"; C. C. Potwin, Electrical Research Products, Inc., New York, N. Y., 
and B. Schlanger, New York, N. Y. 

Successful design of the motion picture auditorium involves the effective co- 
ordination of both auditory and visual requirements. Past practice has favored 
vision and decorative treatment, usually leaving the acoustical problem as a 
final consideration. 

In this paper a study is made of the basic outline, the volume, and the detailed 
form of a motion picture auditorium, to show that auditory and visual require- 
ments can both be met successfully if they are treated with equal importance in 
fundamental planning. This does not preclude the ability to obtain economical 
design and pleasing architectural form. Actually, the study proves that eco- 
nomical construction and creative architectural forms are more readily inspired. 

"Chemical Analysis of an MQ Developer"; R. M. Evans and W. T. Hanson, 
Jr., Kodak Research Laboratories, Rochester, N. Y. 

The maintenance of developer activity over a long period of time is among the 
most important problems of a motion picture laboratory. The developer is 
oxidized by the silver halide in the emulsion and by air. When known amounts 
of these two oxidizing materials react with the developer, simple calculations, 
which were presented in a previous paper, are sufficient to determine the equi- 
librium condition of the developer as well as the replenisher formula to give a 
chosen equilibrium. Under ordinary conditions there are large variations in the 
amount of developer oxidation. A chemical analysis immediately detects any 
deviation from the correct equilibrium and permits readjustment of the replen- 
isher formula. Chemical analyses are presented which require a minimum of 
equipment and time. In most cases, ease of manipulation and speed have been 
considered as more important factors than a high degree of accuracy but in all 
cases the methods are capable of giving results to an accuracy of five per cent 
or better. Whenever possible the analyses are colorimetric in nature, the mea- 
surements being made on an instrument called an Opacimeter. One operator can 
make a complete analysis in about half an hour. Analysis for any one con- 
stituent may be made in a much shorter time. It is emphasized that no one 
control variable is significant for specifying the activity of a developer. Sensito- 

Oct., 1938] FALL CONVENTION 433 

metric curves are included demonstrating the time lag in pH equilibrium but not 
in photographic equilibrium when hydroxide is added to or released in the de- 
veloper. The aim of chemical control is to insure a constant condition of the 
developer and thus constant photographic quality, rather than to determine the 
degree of development. 

"Opacimeter Used in Chemical Analysis"; R. M. Evans and G. P. Silberstein, 
Kodak Research Laboratories, Rochester, N. Y. 

The opacimeter is an optical instrument designed to measure the light trans- 
mission of a colored or turbid solution. A Loewenthal photronic type light- 
sensitive cell connected to a microammeter is used to measure the intensity of 
the light transmitted by the solution under test. The light intensity falling upon 
the sensitive cell is kept within a fixed range by varying the distance of the cell 
from the source. The instrument is arranged so that a 30-cc. test tube or a 
300-cc. Kohle flask may contain the reaction mixture. The results of analyses 
are determined from calibration curves prepared from known solutions. 

"Some Television Problems from the Motion Picture Standpoint"; G. L. 
Beers, E.W. Engstrom, and I. G. Maloff, RCA Manufacturing, Co., Inc., Camden, 

There are certain characteristics of television that have counterparts in motion 
pictures. Also, motion picture film and motion picture practice are applicable 
to television; some of the problems and limitations are outlined. 

The following television image characteristics are briefly discussed: (1) 
number of scanning lines and the relationship to image size and viewing distance ; 
(2} number of frames; (3) interlacing. The effect of film and optical system 
limitations upon reproduced television images is illustrated by photographs. 
Curves are given showing the spectral characteristics of Iconoscopes. The 
screen color characteristics of Kinescopes are discussed. The overall range and 
gamma characteristics of a television system are reviewed. 

"Unidirectional Microphone Technic"; J. P. Livadary, Columbia Pictures 
Corp., Hollywood, Calif., and M. Rettinger, RCA Manufacturing Co., Inc., Los 
Angeles, Calif. 

The paper contains a description of the construction of the unidirectional 
microphone, and an equation is obtained showing the cardioid directional re- 
sponse for this microphone. 

Four definite advantages are listed for the use of this microphone in the re- 
cording of sound in motion picture studios. These advantages are (1) attenuation 
of undesirable sounds striking the microphone from the tear; (2) lack of frequency 
discrimination for sounds striking the microphone within its solid cone of recep- 
tion because of the directional response of the microphone, which is practically 
independent of frequency; (3) the greater permissible microphone distance to 
obtain the same ratio of direct to reflected sound that exists at the position of a 
pressure-operated transmitter; and (4) the large solid angle of reception, which 
allows the use of fewer microphones to cover an action. 

Six illustrations are given to show how this transmitter may be used to ad- 
vantage under specific set conditions, and four diagrams illustrate its use for the 
recording of various types of music. 


"A Super Sound and Picture Printer"; O. B. Depue, Burton Holmes Films, 
Inc., Chicago, 111. 

An improved contact printer for the continuous printing of 16-mm. sound und 
picture has some new film-handling features. The film may be threaded over 
either picture sprocket or sound printing drum or both, according as the negative 
is of the double- or single-film system. The picture is printed while the film is 
supported by a sprocket engaging the perforated edge of the film. At the same 
time, the other edge is supported on a roller tread and flange which, instead of 
being carried on the extended sprocket shaft, has its own ball-bearing mounting 
and is driven by the film. In this way the section of shaft is eliminated from the 
center of the sprocket, making possible a better location of the printing illumina- 
tion beam. Thus it is possible without the addition of complicated optical ele- 
ments to have the illumination fall perpendicularly upon the film at the center of 
the area of contact between negative and positive. The sound printing takes place 
similarly on a nearby drum. Provision is made at this point for the insertion of 
an optical filter. Lamp current is supplied by a built-in motor-generator set at 
any required voltage between 90 and 130. 

The printer is driven through a rubber disk vibration filter. All bearings are 
either enclosed grease-packed ball bearings or "oilite" oilless bronze. Sprockets 
are made of stainless steel. The electrical system is protected by the use of an 
overload cut-out instead of fuses 



Details of the Convention are given on page 421 of this issue of the JOURNAL. 
The Tentative Papers Program will be mailed to the membership of the Society 
about the middle of October. Members who plan to attend the Convention are 
urged to return their hotel reservation cards as promptly as possible in order to be 
assured of satisfactory accommodations. 


Several meetings of the Sub-Committee on Projection Room Plans were held 
during the summer, the last one being on September 9th, at the office of the 
Society. The result of this work was the completion of the third revision of the 
Projection Room Plans, which, together with the proposed revision of the NFPA 
"Regulations for Handling Nitrocellulose Film," completed by the Committee 
several months ago, will form the report of the Projection Practice Committee 
to be presented at the Detroit Convention. 

A meeting of the entire Committee was held on September 15th to edit a pre- 
liminary draft of the report, and another meeting will be held on October 13th 
to approve the final draft. 


On Thursday, Septembei 20lh, at the meeting rooms of The Western Society 
of Engineers, the Mid-West Section of the Society held its first meeting of the 
season. Mr. Richard Leitner of the Gumbiner Syncro-Sound, Inc., of Los Angeles 
presented a paper describing " A Professional 16-Mm. Sound-on-Film Camera." 

The meeting was well attended and an interesting discussion followed the pres- 


At a recent meeting of the Admissions Committee, at the General Office of the 
Society, the following applicants for membership were admitted to the Associate 
grade : 

485 California St., 

San Francisco, Calif. 
669 Los Lomas Ave., 

Pacific Palisades, Calif. 

11204 Brookhaven St., 
West Los Angeles, Calif. 


Rua Plombagina 328, 
Bello Horizonte, 

Estado de Minas, Brazil. 

No. 6 Flat Hackney Manor, 
360 Carlisle St., 
St. Kilda S2, 

Victoria, Australia. 




[J. S. M. P. E 


1108 So. Shenandoah St., 

Los Angeles, Calif. 
Via Sabotino, 

2 Rome, Italy. 

Kodak Aktiengesellschaft, 
Lindenstrasse 27, 

Berlin, Germany. 
63 Marionville Rd., 

Edinburgh, Scotland. 

VIII Gyulaipal U. 5, 

Budapest, Hungary. 

2850 Leeward Ave., 

Los Angeles, Calif. 

Dufay-Chromex Ltd., 
14 Cockspur St., 

London, England. 
2016 E. Firth St., 
Philadelphia, Penna. 


88-35 Elmhurst Ave., 

Elmhurst, Long Island, N. Y. 

c/o Evergreen Pictures, 
Saklat House, 

15 New Queen's Road, 

Combay, India. 
723 Seventh Ave., 

New York, N. Y. 
1976 So. 7 East, 
Salt Lake City, Utah. 

P. O. Box 101, 

Arecibo, Puerto Rico. 

San Marco 557, 
Venezia, Italy. 


Adams' Building, 
484 George St., 
Sydney, Australia. 


Parlatone Hispano Filipino, 
Motion Picture Co., 
Manila, P. I. 

138 28th St., 
Wheeling, W. Va. 

Kodak Limited, 
Stockholm, Sweden. 

6331 Florio St., 
Oakland, Calif. 


Viale Vittorio V. 24, 
Milan, Italy. 


5718 Hillcrest Drive, 
Los Angeles, Calif. 


90 E. Palmer Ave., 
Detroit, Mich. 

P. O. Box 263, 
Syosset, N. Y. 

In addition, the following applicants have been admitted by vote of the Board 
of Governors to the Active grade. 

Fairmont Theater, 
Fairmont, W. Va. 

6 Stanmore Hall, 

Middlesex, England. 



Estudios San Miguel, Pinewood Studios, 

Bella Vista F.C.P., Iver Heath, 

Buenos Aires, Argentina. Bucks', England. 


923 Hardesty Blvd., 
Akron, Ohio. 


The following are available from the General Office of the Society, at the prices 
noted. Orders should be accompanied by remittances. 

Aims and Accomplishments. An index of the Transactions from October, 
1916, to December, 1929, containing summaries of all articles, and author and 
classified indexes. One dollar each. 

Journal Index. An index of the JOURNAL from January, 1930, to December, 
1935, containing author and classified indexes. One dollar each. 

SMPE Standards. The revised edition of the SMPE Standards and Recom- 
mended Practice was published in the March, 1938, issue of the JOURNAL, copies 
of which may be obtained for one dollar each. 

Membership Certificates. Engrossed, for framing, containing member's name, 
grade of membership, and date of admission. One dollar each. 

Lapel Buttons. The insignia of the Society, gold filled, with safety screw back. 
One dollar each. 

Journal Binders. Black fabrikoid binders, lettered in gold, holding a year's 
issue of the JOURNAL. Two dollars each. Member's name and the volume 
number lettered in gold upon the backbone at an additional charge of fifty cents 

Test- Films. See advertisement in this issue of the JOURNAL. 



Professor Norman McClintock, distinguished photo-naturalist and member of 
the Society, died of a heart attack at Orlando, Florida, on February 26, 1938. 
Professor McClintock joined the staff of Rutgers University at New Brunswick, 
N. J., in 1931 as a special lecturer, and retained the position to the time of his 

Norman McClintock received his B.A. degree from Yale University in 1891. 
He became interested actively in motion picture photography of insect life, plant 
life, wild birds, and big game about 1914. For nearly a quarter of a century he 
devoted his full time to these studies, and was one of the first to make fine quality 
motion picture studies of bird and plant life. His services as a lecturer were much 
in demand because of the remarkable films which he showed and the unusual per- 
sonality of the speaker. 


No one could talk to Professor McClintock for more than a few minutes with- 
out feeling some of the joy and thrill which he got from the work in which he was 
engaged. Professor McClintock spoke on several occasions at the semi-annual 
conventions of the Society and always delighted his audiences with his rare wit 
and anecdotes of his personal experiences. 

Some of the time-lapse motion pictures of the growth of plants are considered 
classics in this field. He devised several ingenious devices for controlling auto- 
matically the duration of exposure and illumination for these investigations. 

The world has lost a unique research worker in the field of natural history. 




Volume XXXI NOVEMBER, 1938 Number 5 


Electrical Networks for Sound Recording F. L. HOPPER 443 

A Non-Intermittent Projector for Television Film Transmission 

H. S. BAMFORD 453 

Silent Gasoline Engine Propelled Apparatus. .J. E. ROBBINS 462 
A Technic for Testing Photograpihic Lenses . . . . W. C. MILLER 472 

Report of the Projection Practice Committee 

Projection Room Plans 480 

Proposed Revision of Regulations of the National Board of 
Fire Underwriters for Nitrocellulose Motion Picture Film 
as Pertaining to Projection Rooms 498 

New Motion Picture Apparatus 

A New Sound System G. FRIEDL, JR. 511 

Variable Matte Control (Squeeze Track) for Variable-Den- 
sity Recording .G. R. CRANE 531 

An Improved Editing Machine J. L. SPENCE 539 

Current Literature 542 

Abstracts of Papers for the Detroit Convention 544 

Society Announcements 547 





Board of Editors 
J. I. CRABTREE, Chairman 



Subscription to non-members, $8.00 per annum ; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscriptions or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 
Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 

West-Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1938, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is 
not responsible for statements made by authors. 


President: S. K. WOLF, 1270 Sixth Ave., New York, N. Y. 
Past-President: H. G. TASKER, 5451 Marathon St., Hollywood, Calif. 
Executive Vice-President: K. F. MORGAN, 6601 Romaine St., Los Angeles, 


** Engineering Vice-President: L. A. JONES, Kodak Park, Rochester, N. Y. 
Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 
Financial Vice-President: E. A. WILLIFORD, 30 E. 42nd St., New York, N. Y. 
Convention Vice-President: W. C. KUNZMANN, Box 6087, Cleveland, Ohio. 
Secretary: J. FRANK, JR., 90 Gold St., New York, N. Y. 
Treasurer: L. W. DAVEE, 76 Varick St., New York, N. Y. 


*J. O. AALBERG, 6920 McKinley St., Los Angeles, Calif. 
*M. C. BATSEL, Front and Market Sts., Camden, N. J. 
**R. E. FARNHAM, Nela Park, Cleveland, Ohio. 
*G. FRIEDL, JR., 90 Gold St., New York, N. Y. 
*A. N. GOLDSMITH, 444 Madison Ave., New York, N. Y. 
**H. GRIFFIN, 90 Gold St., New York, N. Y. 

**A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 
*S. A. LUKES, 6427 Sheridan Rd., Chicago, 111. 
*Term expires December 31, 1938. 
**Term expires December 31, 1939. 


Summary. Electrical networks are employed in sound recording for modifying 
and limiting the frequency-response characteristic. The necessity for their use, ap- 
plication, and design is described. Particular emphasis is placed upon the constant- 
resistance type of structure. 

The design philosophy for a transmission system to translate the 
spoken word or music into some form of record has been one pre- 
dicated upon the use of elements having uniform response-frequency 
characteristics. In sound recording a number of factors exist that 
necessitate certain modification and limitation of these character- 
istics in order to achieve pleasing results. Some of these factors are : 

(a) The effects due to the acoustical conditions surrounding the point of 

(&) The response characteristic of the microphone. 

(c) The properties of the modulating device and noise-reduction system. 

(d) In re-recording, the ability to compensate for defects occurring in record- 
ing, and the introduction of characteristics providing certain dramatic effects. 

All these alterations of characteristic are accomplished by the use 
of various passive electrical networks. Those employed for modifica- 
tion make use of the properties of resonant circuits, combinations of 
capacity or inductance with resistance, or the grouping of such ele- 
ments into the lattice or bridged- T type of constant-resistance net- 

Limitation of the frequency-response characteristic is accomplished 
by grouping inductance and capacity elements into high- and low- 
pass filter structures. Occasionally, constant-resistance networks, 
alone or in combination with filter sections, are used. 

The choice of a particular type of network depends upon the re- 
quired insertion loss, the impedance of the circuit in which it is to 
operate, and the reaction of the network's impedance characteristic 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received 
April 18, 1938. 

** Electrical Research Products, Inc., Hollywood, Calif. 


444 F. L. HOPPER [j. s. M. P. E. 

upon the frequency-response of the equipment associated with it. 
The last factor is of considerable importance when a network is con- 
nected to the input circuit of an amplifier, since frequently the 
amplifier response is altered when working into an incorrect or vary- 
ing impedance. A comparable condition may exist when a network 
is operated on the output of an amplifier, particularly if the amplifier 
output stage contains pentodes. In addition, if a number of net- 
works are to be connected in tandem, the constant-resistance type is 
advisable. Generally, one end of a constant-resistance structure 
must be terminated ideally if terminal effects are to be made negli- 
gible. Several constant-resistance networks in tandem will add 
their respective loss characteristics without interaction provided 
they are designed for the same nominal terminating resistance, and 
are actually terminated in this resistance at one end. If neither end 
is well terminated, or if some non-constant resistance network is 
included in the chain, the overall loss characteristic will show inter- 
action effects. The generally desirable features of networks of this 
type have resulted in their nearly universal use for modifying the 
characteristic in sound recording. 

These same criteria apply to the choice of filter structures for 
limiting the frequency-response characteristic. Usually the filter is 
composed of combinations of constant-^ and Af-derived sections, 
since the constant-resistance network does not usually introduce in- 
sertion loss with sufficient rapidity. A number of the commonly 
used types of networks, their functions, types of service, and char- 
acteristics are given in Table I. 

The networks shown by no means constitute a complete list, but 
may be regarded as representative of those in use in many of the 
studios. Among other types having more limited use are those for 
equalizing monitoring systems and a number of special types em- 
ployed in re-recording, which permit attenuating certain restricted 
bands of frequencies to achieve special effects. 

The designs of filters used for limiting the frequency-response char- 
acteristic are well covered in the literature. 1 Design data pertaining 
to the constant-resistance type of network are probably not so well 

Since this structure has so many applications in the recording field, 
it is of interest to consider its design. We may choose the bridged- T 
form, since nearly all transmission circuits wherein such equalizers 
are employed are grounded on one side. In addition, this type re- 








Dialog Equalizer Compensates for stage con- Recording 

Microphone Equal- Compensates for micro- Recording 
izer phone irregularities or cer- 

tain acoustical response ef- 

Depends upon 

Presence Equalizer Corrects for certain Acous- Recording 
tic Pick-up Effects. 

Pre-Equalizer Increases highs subse- Recording and 

Post- Equalizer quently attenuated in re- Reproducing 

producing. Used to re- 
duce noise. 

Film Equalizer Compensates for film Re-recording 


Low-Frequency Permits adjustment of re- Re-recording 

Corrective sponse for corrective or 

dramatic effects. 

High-Frequency Permits adjustment of re- Re-recording 

Corrective sponse for corrective or 

dramatic effects. 





High-Pass Filter Limits low-frequency re- Recording and 
sponse. Re-recording 

Low-Pass Filter Limits high-frequency re- Recording and 

sponse, depending partially Re-recording 
upon modulating devices 



[J. S. M. P. E. 

quires fewer elements than the lattice structure. The general form 

of the network is shown in Fig. 1 

FIG. 1. Simple bridged- T network: 
A = A = R/c; B = (C*-1)R/2C. 

The resistances A, A, and B form 
a conventional T type of "pad." 
This may be of either the finite or 
infinite loss type, depending upon 
the design problem. The ele- 
ment Zu is arbitrarily chosen as 
the independent variable deter- 
mining the transmission charac- 
teristic of the network. The 
elements comprising Z n may be 
reactive, resistive, or a combina- 
tion of both. Networks used 
in sound recording usually em- 
ploy elements consisting essen- 
Consequently, this case will be con- 

tially of pure reactance, 
sidered first. 

The factors determining the insertion loss, in decibels, of a given 
network are: 

(a) The loss of the T pad. 
(6) The impedance of the reactive element Zu. 

(c) The iterative impedance, R, of the circuit in which the network is to 

An equation relating these quantities is derived in the appendix of 
this paper. In Fig. 2, a family of curves representing various pad 
losses has been plotted as a function of the impedance Zu as abscissa, 
and the corresponding network insertion losses as ordinates. R is 
assumed to be 500 ohms. The relations between Z\\ and Z%\ t their 
use as elements in various networks, and the characteristics of such 
networks are shown in Fig. 3. 

In the design of a particular network Fig. 3 enables a choice of 
element Zu to effect a certain shape of characteristic. If the re- 
quired characteristic is somewhat complex, it may be necessary to 
achieve the final desired characteristic by employing one or more 
networks, the sum of their individual characteristics resulting in the 
required one. In addition, the following data are necessary : 

(a) The maximum required insertion loss, determining the pad value. 

(&) The insertion loss at some particular frequency which effectively deter- 
mines the shape of the insertion loss characteristic. This in turn determines the 
value of Zu (from Fig. 2) and from Fig. 3 the values of the reactive elements L and 



C may be computed. From these, the impedance Z u may be computed for other 
frequencies and the insertion loss read from the charts of Fig. 2. 

An example of such a computation is given in the appendix. 

It is apparent from an inspection of Fig. 2 that the insertion loss 
approaches the pad loss for large values of the impedance Zn, and 
hence does not become infinite. If the T pad is of the infinite-loss 

x-x - R 





2 3 456789 IpOO 2 


9 10,000 

FIG. 2. Constant-resistance network design chart (curves give insertion loss 
in a 500-ohm circuit). 

type, i.e.,ifA=A=R and B is zero, the insertion loss of the network 
becomes increasingly large as Zn increases, approaching infinity as 
Zn approaches infinity and Z>n approaches zero. A design curve for 
this type of structure is included in Fig. 2. 

Another special condition having practical use in the design of 
variable attenuators is the case when Zn is resistance only. This 
affords the opportunity of designing a bridged- T type of attenuator 



[J. S. M. P. E. 

having constant-resistance properties. Design information for this 
case is also presented in Fig. 2. 

Phase-shift introduced into a circuit by the resistance-arm bridged- 
T structure shown in Fig. 1 will usually be less than 40 degrees for 



Zu Zzi 






00 Li 







H xZ 2 ,-R 2 

TYPES 1 & It 

L,C,-L 2 C 2 

J=2 = R 2 

FIG. 3. Equalizer chart. 


2H~y L 2 C 2 

networks employing finite pads, and will approach 90 degrees as a 
maximum for networks employing an infinite-loss type of pad. 

The wide adaptability of constant-resistance networks to the 
equalization requirements of sound recording is best demonstrated 
by their wide-spread use. The methods outlined here simplify the! 
design of such networks to meet specific characteristics. 



Referring to Fig. 1, the general form of the bridged- T network, the resistances 
R/c, R/c, and (c* l)R/2c form a conventional T type of pad. The value of 
c for a given pad loss is given by 

Pad loss in db. = 20 log - = 20 log n (1) 


where *'] = current in the load resistance when the pad is not in the circuit. 

i z = current in the load resistance when the pad is inserted in the circuit. 

c is then defined as 

= ^\ (2} 

For the network, Z n is arbitrarily taken as the independent variable determin- 
ing the propagation constant. Z 2 i is dependent upon Zn through the relation 

Z u X Z 21 = R 2 (3) 

The propagation constant of the network is given by Zobel 2 as: 

, (c + 1) Zn 
2 ~R 


2 R 

From eq. 4 both the attenuation and phase constants may be obtained since 

m +jn (5) 

and e a = Aw 2 + w 2 (0) 

where a is the attenuation constant in napiers. 
The phase constant in degrees is given by 

tan/3 = - (7) 


A general solution of eq. 4, assuming that Zn is composed of both reactance and 
resistance gives 

Z u = ^Tcos0 R == R r -cose + e (8) 

6 = angle between the resistance and reactance components of Z u . For the 

450 F. L. HOPPER [j. s. M. P. E 

case when Z\\ is reactance only eq. 8 may be simplified, since 6 is 90 degrees an 
cos = 0. Eq. 8 then becomes 

Eq. 9 may be simplified for direct substitution by converting the attenuatio: 
in napiers to attenuation in decibels, resulting in 

where db. = the insertion loss of the network. 

Zu = impedance in ohms of the reactive element of the network. 
Eq. 10 has been plotted for design purposes assuming R is 500 ohms in Fig. 2 
For the infinite-loss type of pad c = 1, and the pad resistances become A = 

A = R, and 5 = 0. Substituting c = 1 in eq. 10 gives 

Zn = R Ve* - 1 (11) 

This is plotted in Fig. 2, assuming R to be 500 ohms. 

Referring to eq. 8, if no reactance is involved but only resistance, 6 is zero de 
grees, and cos = 1; hence 

For an infinite-loss type of pad c = 1, r = s = 1 and eq. 12 becomes 

Z n = (e - 1) (15) 

This equation permits the design of a bridged- T type of attenuator having con 
stant-resistance properties. It has been plotted in Fig. 2. 

The phase change introduced by a network employing a finite pad may be com 
puted from eq. 7, and, for the case where Z\\ is reactance only, becomes 

Examples of the use of this design data follow. 

Low-Frequency Attenuating Network. Assume that the requirements for thiij 
network are an insertion loss of 4 db. at 100 cycles, and about 8 db. at 20 cycles) 
when connected in a 500-ohm circuit. Reference to Fig. 3 indicates that Zi, 
should be a capacity C, and Z 2 i an inductance L. Since the maximum require^ 
loss is 8 db., a pad of that value is chosen. The insertion loss at 100 cycles deter 


mines the value of Z n or C as follows: From Fig. 2 for an 8-db. pad and 4-db. 
insertion loss Z n is 490 ohms. Since Zn =- 1/taC and w at 100 cycles is 2v X 100 
nre have 

= 3.24 mfd. 

coZn 628 X 490 
md L = R 2 C = 500 2 X 3.24 X 10~ = 0.81 h 

having determined these constants the insertion loss at other frequencies may be 
: ound as follows : 

Freq. o>C wC ~ ^t? 

20 125 407X10-' 2460 7.6db. 

40 252 817 1220 6.8 

100 628 2030 490 4.0 

200 1256 4060 246 1.7 

Equalizer for Re-Recording System to Simulate Poor Radio Quality. Assume that 
he requirements for this network are no insertion loss at 800 cycles, 7 db. at 300 
ycles, and with increasing insertion losses at both extreme low and high frequen- 
ces. The network is to operate in a 500-ohm circuit. Fig. 3 indicates the choice 
if a series-resonant circuit comprised of LI and Ci for Zn, and an anti-resonant 
:ircuit composed of L 2 and C 2 for Z 2 i. Since the network losses are to increase 
>utside the specified limits, an infinite-loss type of pad is used. The values of 
*i, Ci are determined from the insertion loss requirement of 7 db. at 300 cycles 
^ follows: 

Since f r occurs at 800 cycles, the frequency for no insertion loss, 

4X1 " 

.nd Zn for a 7-db. insertion loss with an infinite-loss pad (from Fig. 2) is 990 ohms. 


L, CiR* = 0.464 X 10- X 500' = 0.116 h. 

nd ft = . 0.345 mfd . 




Insertion losses at other frequencies are: 










Ins. Loss 
(Fig. 2) 



.39 X 10 6 



































































T. E.: "Transmission Networks and Wave-Filters," D. Van N 
strand Co. (New York). 

8 ZOBEL, O. J.: "Distortion Correction in Electrical Circuits," Bell. Sy 
Tech. J., VII (July, 1928), No. 7, p. 438. 



Summary. A continuous machine is described for the projection of images from 
Im into the pick-up camera for television transmission of motion pictures. The 
imera tube can be either of the instantaneous or the storage type. The images are 
wident upon the cathode during scansion and the optical image transition interval 
> less than the scanning flyback interval with which it is synchronized. Certain ad~ 
intages are taken in the construction of a double-lens disk type of optical compensator 
obtain an image steadiness determined only by the number of lenses per disk, such 
'rors as are introduced by lens setting and gearing being negligible. 

The telecine projector to be described operates upon the principle 
f optical compensation as the film moves continuously through the 
1m gate and can, therefore, be called a continuous or non-inter- 
littent type of machine. As a telecine projector, it is applicable 
trictly to the projection of images from film for television pick-up, 
nd the images so projected are substantially stationary. 

Fig. 1 is a photograph of such a machine, constructed to project 
:om 3 5 -mm. sound recorded film, and similarly the principle of 
peration can be applied to 16-mm. sound-film projection when the 
umber of images per second is 24. 

The machine is operable with a pick-up tube of either the in- 
;antaneous or the storage type. By instantaneous type of pick-up 
Ube is meant a tube wherein the elemental signal leaving the tube is 
^presentative of the optical image element at the instant it is scanned, 
nd is of an intensity determined by the light-intensity, sensitivity 
E the cathode surface, the element area, and the time required to 
:an the element area. Obviously, the absence of an optical image 
pon the cathode during the whole or part of the scansion interval 
isults in either a total blank or an image with a horizontal blank bar 
le width of the image, and of a height determined by the interval of 
ptical image cut-off. 

* Received July 1, 1938. 
** Farnsworth Television, Inc., Philadelphia, Pa. 




[J. S. M. P. E. 

A pick-up tube of the storage type is one in which the optical 
image incident upon the cathode gives rise to a charge image which 
remains until it is removed by scansion, and the resulting elemental 
signal leaving the tube is representative of the elemental charge 
stored upon the cathode during optical image incidence of an intensity 
determined by the intensity of the light, sensitivity of the cathode 
surface, the element area, the tune required to completely scan one 
frame, and a factor, K. 

The Farnsworth "dissector" is an example of the instantaneous 
type of pick-up tube; the iconoscope, emitron, and image amplifier, 
examples of the storage type. 

FIG . 1 . Telecine pro j ector . 

Such a universal application can be better understood and certain I 
advantages recognized when we consider that the projected image is | 
stationary upon the cathode of the pick-up device and has a duration j 
equal to the scanning time, changes from image to image occurring i 
only during the scanning flyback interval. According to present j 
standards, the time allowed for flyback between scansions is 10 per 
cent of the field scansion tune, or Veoo second. Such a requirement 
should make obvious the need for a machine of the continuous type ! 
in which optical image transition can be accomplished at very high j 
speed as compared with the intermittent type projector, wherein the I 
optical image transition tune is limited to a speed determined by the , 
ability of the film to withstand the effect of the acceleration with in- j 
creasing tension necessary at the film gate to maintain steadiness. ; 

Nov., 1938] 



A 72-degree intermittent jerking the film into its successive positions 
in Vwo second is by no means a slow intermittent movement. In 
addition, various methods of selection of optical image sequence can 
be simply accommodated, including the method wherein successive 
images are superimposed for a brief transition interval, during which 
interval the total light is kept constant by the selector disk. 

Many systems of optical compensation have been designed and 
tried in the past for theater projection, using lenses, prisms, or mir- 
rors, and many more systems can be conceived, using them in combi- 
nation, giving almost perfect first-order results. However, the 
first-order derivation is not sufficient to predict the overall per- 
formance of the system. The presence of third-order aberrations in 
sufficient magnitude will destroy what might look to be a perfect 

FIG. 2. Illustrating method of optical compensation. 

design. In addition, the physical setting of the component elements 
and the mechanical drive of the system are obviously of extreme im- 
portance. The effects upon the projected optical image by a machine 
in which these faults are present are unsteadiness during image in- 
cidence and lack of coincidence of successive image frames. Both in 
effect constitute image jump, and their effects are more destructive 
in telecine projection due to the present system of interlacing than 
they would be for direct viewing or non-interlaced scanning. 

Some systems lend themselves admirably to the fulfillment of the 
above-described requirements, while others do not. It is not possible 
in a limited space, nor would it be of general interest, to discuss in 
detail various systems of optical compensation and their qualities 
and failings, though it might be well to inject some general con- 
siderations. A system in which the optical compensator is a single 
unit is going to require that the driving gear be extremely accurate; 

456 H. S. BAMFORD [j. s. M. P. E. 

many times more accurate than the pair of gears required to drive 
the optical compensator of the symmetrical double-unit type. That 
the optical elements can be corrected with no great difficulty, if at all, 
is another consideration. The following is intended to indicate an 
approach to the ideal optical compensator for the particular purpose 

Fig. 2 illustrates a method of optical compensation wherein the 
motion of a lens is made to compensate for film motion, so that the 
projected image is stationary, and equation 1 gives these required 
motion relationships : 

* = -y (l/m - 1) (i) 

di = film displacement. 
y = lens displacement. 
m = magnification. 

Equal numbers of lenses mounted upon two oppositely rotating 
disks in optical mesh can be made to constitute a succession of well 
corrected projection objectives of very closely matched focal length 
and magnification. By optical mesh is meant that each lens on the 
one disk overlaps a lens on the other, so that they form substantially 
a symmetrical objective. As the disks rotate through the necessary 
angle, the component lenses move apart in equal amounts in opposite 
directions, and by selecting a slightly different focal length for the 
one disk the effects of these horizontal displacements upon the pro- 
jected image are mutually annulled. 

Two components of a composite lens contribute to the total mag- 
nification of the system in amounts : 

mfi +/ 2 


fi +/2 - a 

fi = focal length of the first lens. 
/ 2 = focal length of the second lens. 
Wi = magnification by the first lens. 
W2 = magnification by the second lens. 
a = separation of the component lenses. 

The displacement of an image point by the displacement of a lens is : 

x = y (1 - w) (4) 

m = mim 2 = magnification of the system. 
Therefore, for complete annullment of the horizontal displacements 


of the two component lenses, the focal lengths must be related as 
follows : 

/,./,- iOSL+i) (5) 

m 1 . 

Should the focal lengths of the two component lenses be the same, 
fa = / 2) the horizontal displacement error can be computed from 
equation 6, wherein yi = y 2 : 

E H 

2/1 a 

EH horizontal displacement error. 

y t = horizontal displacement of lens No. 1. 

y 2 = horizontal displacement of lens No. 2. 

Substitution in equation 6, for the particular system used, will indi- 
cate a negligible value of E H when the focal length of the lens on the 
front disk is similar to that of the lens on the rear, with consequent 
advantages in construction. 

The vertical component of the lens motion is parallel to the motion 
of the film and constitutes to an acceptable degree the compensating 
motion, y, as set forth in equation 1. This vertical motion of the 
lens varies as the sine of the angle of rotation of the disks and is, 
therefore, nonuniform, while the film is moved through a plane gate 
at a uniform rate. Obviously, the projected image will not be per- 
fectly stationary, but will be periodically displaced vertically a small 
amount, such amount being termed the vertical displacement error. 
This vertical displacement error contributes to the overall image 
jump. By the proper selection of the lens disk radius, a minimum 
vertical displacement error can be derived for a given magnification 
and angular projection interval of the disks. The number of lenses 
per disk determines the angular projection interval, while the number 
selected is determined by the allowable vertical displacement error, 
and the allowable horizontal separation of the overlapped component 

The use of a curved film gate in allowing an average correction of 
the lens disk sine error introduces a displacement error by virtue of 
its distorting effect. Defocusing also results when the image is pro- 
jected from film running through a curved gate onto a plane. Ob- 
viously, lens curvature can only make an average correction for gate 
curvature, while curvature of the cathode must include consideration 
of the electron optical system. 

458 H. S. BAMFORD [j. s. M. P. E. 

In consideration of the following, the diameters of the lenses are 
such that only the required amount of light is projected, and not a 
needless excess; and the system magnification, determined by the 
lens disk radius, is such that the projected image needs little modifica- 
tion by a fixed-axis auxiliary lens. The third-order aberrations all 
vary as some function of the lens aperture. The magnification of 
the lens disk gear errors is* proportional to the ratio of the lens disk 
diameter to the pitch diameter of the gear. Still more reasons can be 
cited to indicate the importance of the correct determination of the 
lens aperture; the reasons given above are obviously most important. 

The mounting of the lenses upon the disks in their correct positions 
is made possible to a reasonably high degree of precision by virtue of 
the fineness of lens correction and uniformity. The grinding, cen- 
tering, and edging of the component elements must be well done and 
a reasonable uniformity maintained in element thicknesses. A high 
degree of uniformity of focal length is facilitated by the ability to 
modify slightly when cementing the component elements. The 
cemented achromat is mounted in a holder, preferably of the same 
metal as the disks, and gripped so that there will be no strain. Slip- 
ping after the settings are made, either of the holder on the disk or 
the lens in the holder, must not occur. It is not abnormally difficult 
to mount these lenses in their holders upon the disks spaced from each 
other and similar in radii to within 0.0002 inch. As the effect upon 
the projected image is divided between the two overlapped lenses 
equations 2, 3, and 4 and each lens has its own setting error not ex- 
ceeding 0.0002 inch, the image displacement will be some average not 
exceeding 0.0002(1 m) inch, or possibly zero when the setting errors 
of the two lenses are equal and opposite. A detailed description of 
the alignment procedure is impossible in a limited space; it is suf- 
ficient to say that the order of accuracy involves in the aligning in- 
strument a good degree of thermal and mechanical stability. 

The lens disks are geared directly to the film drive sprocket shaft 
so that the errors due to nonuniformity of drive are not present in 
the projected image. The gear train from the film drive sprocket to 
the lens disks is so designed that annullment of eccentric error is 
accomplished to a high degree and the transmission of residual errors 
is reduced in proportion to the ratio of the pitch diameters of the 
common shaft gears. The four gears driving the two lens disks can 
be so arranged that their eccentric errors are subtractive by virtue of 
the optical mesh. Such advantages of gear arrangement can not be 

Nov., 1938] 



taken in most other systems with consequent requirements of almost 
impossible precision in gear cutting and attendant high cost. The 
gears are bronze mating with steel cut on a gear shaper and enveloped 
to give what might be called a commercial high-precision gear. En- 
veloping, or shaving, as it is sometimes called, is very effective in 
finishing a well cut gear so as to correct eccentricity, nonuniformity 
of tooth spacing, and involute profile, beside smoothly finishing the 



FIG. 3. Selection disk in relation to lens disks. 

tooth faces. This smooth finish has much to do with maintaining 
accuracy over a period of time. 

The driving of the film through the film gate constitutes another 
problem to which attention must be given. Due to the fact that the 
image is projected while the film is moving, variations in that motion 
naturally result in an unsteady image. If the film is pulled through 
the gate by a sprocket, and the sprocket teeth do not accurately 
match the film perforations, periodic slipping of the film will result at 
a frequency of 96 per second, for 35-mm. film. Obviously, the 
images projected from a film so driven will have a periodic vertical 
jump. Variation in shrinkage of films according to their age and 



[J. S. M. p. E. 

treatment makes it impossible to determine a fixed sprocket size that 
will give acceptable results. A sprocket with a variable diameter, 
graduated, will accommodate different films and was tried experi- 
mentally with considerable success. That the shrinkage is suf- 
ficiently uniform throughout the reel to satisfy present requirements 
for a given setting has been indicated in the results so far obtained. 
Framing the film in the gate is very simply done with the sprocket 
drive method by increasing or decreasing a loop between the gate 
and the film drive sprocket with a displaceable idling roller. 

The images are projected upon the cathode of the pick-up tube in 
correct sequence for scanning by a predetermined selection of the 

FIG. 4. Operating side of telecine projector. 

projection lenses on the lens disks. Fig. 3 illustrates a method of 
selection in which a disk with spiraled slots rotates directly in front 
of the lens disks occulting all but the desired lens. The spiraled slot 
follows the lens in its downward travel and allows the projection of a 
single frame for a predetermined time, after which time the first lens 
is occulted and the next lens uncovered to project the following frame. 
The selector disk, as shown, is slotted to allow the projection of suc- 
cessive images of such time duration that they can be scanned alter- 
nately two and three times with a transition interval of less than 
Veoo second. By adjusting the phase relationship between the syn- 
chronous projector motor and the projector, the image transition 


intervals are made to coincide with the scanning flyback intervals. 
The above allows scansion of single images with a minimum angular 
projection interval of the lens disks. 

Fig. 4 pictures clearly the operating side* of the telecine projector 
wherein the film is uniformly illuminated in the gate by a Mazda in- 
candescent lamp, an image of the source being projected in the plane 
of the selector disk. A uniformly bright image is maintained during 
the projection interval by constriction of the slots in the selector 
disk according to the lens position in the light-spot. For the machine 
described, the amount of light so projected is in excess of 40 lumens. 
The image size can be modified by adjustments of the low-power 
auxiliary lens shown directly in front of the pick-up tube and the 
telecine camera racking table. Measurements of the image projected 
by the experimental machine indicate that the combined errors con- 
tributed by the gears, lens setting, etc., are negligible and that within 
reading error, image unsteadiness does not exceed 1 / 8 per cent. 


Summary. Problems are discussed connected with the design, construction, and 
operation of electrical generators and water pumps running under full load sufficiently 
silently to permit satisfactory sound recording. The units described were the result 
of demands for silent power equipment for making shots on boats, trains, bus in- 
teriors, inaccessible canyons, etc. As an example of what is sometimes required, one 
of the largest units was installed in the hold of a windjammer used throughout the 
Paramount Production "Souls at Sea" and although the microphone was at times 
directly above (approximately 30 feet) the spot occupied by the generator, no noises were 
picked up by the sound recording equipment. 

Four units are described, namely, one 144-kw. Hispano Suiza, one 57-kw. Lincoln 
Zephyr, and one 41-kw. Ford V-8 generator, and one high-pressure Ford V-8 water 
pump. In each case the entire mechanical unit is rubber-mounted on a sub-frame 
within a semi-airtight compartment constructed of an outer shell of 22-gauge auto- 
body steel, four inches of sound-absorbing material with an inner lining of asbestos 
cloth. The entire exhaust system is water-cooled, employing special mufflers also 
housed within the case. One radiator, mounted outside, cools the water for the engine 
as well as the exhaust. All are practically automatic in operation, with electrical 
governors, temperature regulators, etc. The machines have been in operation ap- 
proximately fifteen months and have required very little service other than normal 

Prior to the advent of sound in motion pictures any reliable source 
of power, regardless of noise, was acceptable for operating generators, 
water pumps, and water churns on the lots as well as on location. 
Sound radically changed the entire condition. It was immediately 
necessary to move the equipment 800 to 1200 feet from the camera, 
depending upon conditions which were aggravated by changes in 
wind direction, difficult set-ups, enclosed canyons, etc. Effects of 
water in motion, ripples, and rain were generally shot sync (sound 
dubbed in later), due to the impracticability of obtaining working 
pressures from these distances. 

* Presented at the Spring, 1938, Meeting at Washington, D. C.; received April 
4, 1938. 

** Paramount Pictures, Inc., Hollywood, Calif. 



Many futile attempts were made, in the years that followed, to 
silence the existing equipment. Failures were caused by the fact 
that openings had to be left on both sides of the machines to insure 
adequate cooling of the engines and generators*. They would function 
properly with everything in their favor but would fail miserably when 
placed in boat holds, railroad cars, small barges, etc. 

After seven years of such difficulties it was quite evident that the 
standards utilized in normal automotive practice would have to be 

FIG. 1. Radiator end, Ford V-8 generator. Note 
rubber mountings along bottom of frame. Fans op- 
erated by independent four-speed Yi-hp. motors. Hole 
between side doors serves as exhaust for main genera- 
tor blower fan exhausting approximately 150 cubic-feet 
per minute. 

abandoned and an entirely new design created. With this in mind 
our Engineering Department set out to build, on paper, the perfect 
power plant that would meet the following requirements : 

(1) Be silent in operation. 

(2) Be foolproof. 

(3) Operate semi-automatically. 

(4) Be light in weight. 

(5) Be compact. 

(6) Maintain constant voltage. 

Very little calculation was necessary to prove that the only way 
to make it run silently would be to operate it in a vacuum, an im- 



[J. S. M. P. E. 


^.s o>.s && 

Si* fife if S 

8 ft 9? v F v p 

| u feH^S5 

.il|al sd 

M P8' 

G G O r" S w 
Q.S W .5 >_ .j 


JS 4>.fa'S ^ d,-S 
wcfi oS F S'w 



practicable solution, of course. A sound-proof case housing the 
engine, coupling, mufflers, and generator seemed to present the next 
best medium. When entirely enclosed, the heat-dissipation problem 
had to be contended with. There could be no- blast of air across the 
working parts, no huge body of water to circulate through the engine, 
as in the case of motorboat applications. All exhaust lines would 
have to be water-cooled. The magnitude of the problem will be 
readily understood when it is explained that approximately 1,200,000 
Btu. per hour had to be carried off the motor alone. 

The generators, in order to comply with requirements 4 and 5, 
would have to be about one-half the normal output size, which is 
satisfactory as concerns portables but not for constant power-house 
service. Due to the fact that the average scene seldom exceeds fifteen 
minutes' duration, a 100 per cent overload is not unreasonable. How- 
ever, these excessive loads do create heat and unless the heat is 
carried away immediately it will transfer from surface to internal 
with an attendant efficiency loss. 

After carefully considering each problem, the final design was ap- 
proved and the work started. For obvious reasons, various sizes were 
built, and will be referred to here as 350 (Fig. 1), 475 (Figs. 2 and 3), 
and 1200 (Fig. 4) ampere machines. These terms are strictly "motion 
picture" and are used in lieu of kilowatts when determining loads. 
Ford V-8 engines were used in the 350; Lincoln Zephyr in the 475 
and Hispano Suiza in the 1200, with standard commercial generators 
of 35-, 50-, and 85-kilowatt capacities. 

The engines selected for the large machines were 300-hp. Hispano 
Suiza, wartime aviation type, picked because of their high output 
per pound of weight and their ability to withstand the punishment 
of long idling periods at 1800 rpm. as well as loads of one-half total 
capacity thrown on and off in rapid succession. Many changes were 
made in the motors before installation, in order partially to modernize 
them. New valves, different valve-springs, battery ignition system, 
modern fuel pumps, new carburetors, higher capacity oil pump, etc., 
were used. 

The engines and the generators, directly connected through 
especially designed pin and rubber flexible couplings, are mounted 
rigidly to a sub-frame which is in turn mounted on the main frame 
through commercial vibration dampeners (rubber in shear). 

(Fig. 5) To the main frame, also mounted on the same type damp- 
ener, are bolted the two vertical ends of the sound-proof case. Four 



[J. S. M. P. E. 

FIG. 4. Radiator end, Hispano Suiza. 

FIG. 5. Operating end, Hispano Suiza, showing 
gasoline tanks, instrument panel, bus bars. Entire 
unit lifts off trailer. 


water and two exhaust lines come through one end, and on the op- 
posite end are located the bus bars and the instrument panel, con- 
sisting of throttle, spark control, circuit-breaker, choke, ammeter, 
voltmeter, rheostat control, governor control? oil gauge, vacuum 
gauge and the switches for gas pump, oil pump, fans, and ignition. 

The top cover, tunnel shaped, fits over these end pieces, resting on 
full-length strips of y2-mch felt and bolts through the same dampeners 
to the main frame. The ends and top cover are fabricated of angle- 
iron framework. The outer cover is 22-gauge auto body steel. Next 
to this is placed a P/Vinch thickness of corkoustic, a sheet composi- 
tion of cork and felt, a 1-inch layer of hair felt, another iVa-inch of 
corkoustic and an inner lining of asbestos cloth. All this is held in 
place by strips of spring steel. 

The measured insulation of the 1200-ampere unit, using the gen- 
erator as a source of sound is 22 db. The effective noise reduction is 
actually more than that due to the fact that valve noises are almost 
completely eliminated, but the high frequencies produced by the 
valve mechanism, while very objectionable during recording, con- 

; tribute a relatively small amount of sound power as measured by a 
noise meter. The actual noise level of the machine at approximately 
three-quarter load, measured thirty feet away, was +60 measured 
with a General Radio noise-level meter using a 70-db. weighting 

The 350-ampere unit, again using the generator as the source of 
sound, is 24 db. The noise level measured at a distance of five feet 

I is +65 measured with a General Radio noise-level meter, using a 

| 70-db. weighting characteristic. 

The exhaust system is comprised of five units (Fig. 6) : the engine 
manifolds, elbows, water-cooled mufflers, outside leads, and the outer 
air-cooled mufflers. The manifolds, mufflers, elbows, and leads are 
all especially designed and are water-cooled. They are made of 16- 
gauge galvanized iron with 1 inch of water around all units. The 
inner mufflers are merely long tanks with perforated baffles spaced 2 

i inches apart. The outer air-cooled mufflers are used only when operat- 
ing in very close quarters. The efficiency of this set-up can best 

! be explained by the fact that normal full-load temperatures, at the 
port, 1300F, are reduced to approximately 120F at the tail pipes. 
This reduction, with the attendant contraction of gas pressures, mini- 
mizes the possibility of drumming and whistling noises. 
The radiator sizes, number and capacities of fans and fan motors, 



[J. S. M. P. E 

inlet and outlet flows, and other cooling factors (Figs. 1, 4, and 7] 
were determined by using the standard formulas and ratios of trans 
ference of metal to water to metal to air plus 15 per cent. The addec 
15 per cent was figured to compensate for the normal loss of radiatior 
by air across the engine and to allow for a longer period of high loac 
time with the fans on low speed. To date, no absolutely silent aii 
delivery fans are available, to our knowledge. The fans used are 2^ 
inches in diameter with eight blades, and are independently driven b> 
Y2-hp. four-speed, 250-, 500-, 800-, and 1100-rpm., d-c., motors con 
trolled by switches on the instrument panel. At top speed each far 

FIG. 6. Hispano Suiza generator plant with engine 
and generator door openings. Note water-cooled ex- 
haust manifold (through left opening) with flexible 
water-cooled connection between manifold and elbow 
running to water-cooled mufflers above. 

actually delivers 4000 cubic-feet per minute. To reduce static pres 
sures, the air is pulled from behind through the radiator and thei 
through the blades. The fan motors are kept cool in this manner anc 
the possibility of chopping noises is also diminished. With this set 
up it is possible to run the unit under full load for 18 minutes allowing 
the water temperature to change from 140 to 190F on the low silen 
fan speed. At the end of the shot, the switches are turned to higl 
speed and with no load the water temperature can be dropped bacl 
to 140 in 4 minutes. 

Under full load, the temperature inside the motor housing seldon 
exceeds 110F. To maintain this temperature, air is drawn througl 
a sound-trap in the floor of the set, up across the generator armature 



FIG. 7. Radiator end Ford V-8 water 
pump; water-cooled mufflers inside box, 
air-cooled mufflers along both sides of radi- 
ator. Fans driven by F-belts off extended 
motor shaft. 

FIG. 8. Pump end, Ford V-8 water pump. Door re- 
moved to show rubber engine mountings, crankcase en- 
largement for greater oil capacity, and space for circulat- 
ing coils for water from outside pump. Brackets on cylin- 
der heads support water-cooled mufflers. Asbestos inner 
lining and spring steel strips for holding insulation in 
place. Automatic engine vacuum-operated pump-primer 
shown just behind coupling. 

470 J. E. ROBBINS [J. S. M. P. E 

and into the carburetor. On the first machines an additional scaven- 
ger system was needed to offset the difference in engine air consump- 
tion at idling speeds. The latest unit, the 475-ampere Lincoln Zephyr 
is built with the motor in a separate compartment over the generatoi 
(Figs. 2 and 3). The air, in this instance, is drawn up through the 
lower compartment into the carburetor. In this manner, no engine 
heat ever reaches the generator and the entire unit runs cooler withoul 
the aid of extra blowers. 

In many recent boat hold installations, this particular design has 
proved especially advantageous. In Souls at Sea, a recent Paramounl 
production, two sets were placed on the second deck, approximately 
12 feet below the main deck. Flumes connected to the front of the 
radiator carried all heat and gases to the rear portholes and outside 
No masks were required by the operators and no sound was detected 
by the microphones. 

The large machines are 12 feet long, 60 inches high, 56 inches wide, 
and weigh 10,000 pounds. They are all electrically governed. The 
governors used can not be obtained commercially. They are espe- 
cially designed such that it is impossible to exceed a predetermined volt- 
age setting. Also, they are so constructed that their throttle opening 
action is instantaneous, which obviously prevents the possibility ol 
decreased voltage which would materially affect the value of the 
light. A 10-volt variation in either direction would be immediate!}; 
detected by the camera. This regulation may not appear difficult, 
However, 50 rpm. on the motor will account for a differential of ap- 
proximately 8 volts. The reaction of the motor when instantly re- 
lieved of two-thirds of its load is similar to what would happen if the 
drive shaft of an automobile should snap while being driven up a 
slight grade with a full throttle at 60 miles per hour. The opposite 
action takes place when loads are put back in like proportions. 

As previously explained, six generators of the same design have 
been constructed in various sizes. To date, the only unit other then 
the previously described generators, is a high-pressure water-pump 
(Fig. 8). This unit employs a Ford V-8 engine and a two-stage 4 X 
4-inch pump. The motor is entirely enclosed, as in the case of the 
generators, but the pump is outside. 

For creating eddies, waves, and water in motion, we have designed 
a portable propeller machine that will be gas-engine driven as described 
above. It will be very silent. No radiator will be used, the water 
being circulated from a pool so that no fans will be required. 


No absolutely silent air mover is available at present. All types 
were investigated at the time of construction and many peculiar 
designs to accommodate squirrel-cage and other types considered be- 
fore going to the accepted multi-blade fan. 

The 1200-ampere machines outside have been used successfully 
200 feet from the cameras; the Lincoln Zephyr, 150 feet; and the 
Fords, 100 feet. Twelve feet was mentioned previously; however, 
that was in connection with a boat where the deck afforded additional 
insulation. Such distances may seem excessive, but for the reader's 
satisfaction, he may set the hand throttle of his automobile at ap- 
proximately 60 miles per hour speed, in neutral gear, start walking 
out in front of the car, and measure the distance when he can no 
longer hear the engine. 


Summary. Different makes of lenses have different properties and characteristics 
that may render a lens good for one purpose and totally undesirable for another. Lenses 
of a given make and series often vary in quality among themselves. To obtain the 
best lens for a specific purpose it is necessary to subject the various makes to tests that 
will reveal their characteristics. Once the type of lens for a specific purpose has 
been chosen, it is of great importance to be able to select the best of that type from a 
group submitted by the manufacturer. 

Equipment and technic used in tests that make such discrimination possible are 
described. A few general hints and precautions are given that will aid in determining 
the characteristics most desirable for various purposes. 

Due to the vast number of lenses available at the present time, the 
prospective buyer is faced not so much with the question of where to 
get lenses as which lenses to choose from the multitude presented to 
him. With so many, each with its various features, it becomes a seri- 
ous task to select a certain make and be sure that it, more than any 
other, possesses the qualities required. It is impossible to detect any 
but the grossest errors by merely holding the lens in the hand and 
looking through it. And since lens makers, in common with most 
other manufacturers, describe their products to the best advantage, 
one is at a loss to know how to decide which lenses possess the char- 
acteristics most desired. 

Lens manufacturers have always been loath to publish critical data 
concerning their products. Until they consent to do so the purchaser 
must find means for himself of determining which of the many lenses 
available possess the qualities that best fill his needs. It is not an easy 
task, especially since the science of optics is avoided by most persons 
as being in the realm of the supernatural and comprehensible to only 
a few chosen master-minds. This is totally unfounded, as the funda- 
mentals required for a working knowledge of lenses and lens testing 

* Presented at the Spring, 1938, Meeting at Washington, D. C. ; received 
Aug. 12, 1938. 

** Paramount Pictures, Inc., Hollywood, Calif. 



are no more difficult to acquire than those required for work in sound, 
electricity, or radio. They have merely been shrouded in a cloak of 
mystery that has frightened away many an interested student. It is 
time that anyone having anything to do with lenses in any capacity 
learns how to tell the good from the bad. This paper gives a few ele- 
mentary tests that anyone can comprehend and carry out, and a few 
simple principles that will be of service to anyone faced with the neces- 
sity of selecting new lenses. 

It is possible to go to great extremes to detect errors in lenses. It 
is therefore necessary first to determine just what extremes are justi- 
fied. 'This depends primarily upon how the lens is to be used and 
what is to be expected of it. Once that has been determined it is pos- 
sible to set up equipment and a technic that will reveal the characteris- 
tics of interest. 

The tests and specifications outlined here are intended primarily for 
use with standard 35-mm. camera lenses. The principles are, how- 
ever, applicable to lenses of other types with slight modifications. 
The tests will be found to be sufficiently searching for ordinary pro- 
duction lenses. Added refinements and still other tests can be made 
when occasion demands. 

Since no lens designer is as yet able to design a lens free from all 
aberrations, every lens is necessarily a compromise between numerous 
errors. Various designers feel differently about which aberrations 
should be sacrificed for others, so that almost every make of lens per- 
forms in its own way. It therefore becomes our task, once we have 
decided what characteristics are most desirable, to choose the lenses 
whose corrections lend themselves most advantageously to our pur- 

More than that, once the type or make has been selected, it is 
necessary to test the individual lenses before they are purchased, to 
eliminate any that fall below certain standards. Lenses of a given 
make vary among themselves as do other commercially manufactured 
products. True, certain tolerances are placed upon them by the 
makers, but it is wise to check each lens to make sure that the manu- 
facturers' tolerances are acceptable. 

It would be unwise to stipulate here certain definite qualities which 
should be required of any lens ; these can be determined best by the 
individual user from experience, personal preference, and the demands 
of the job at hand. A few of the more general characteristics common 
to lenses will be mentipned and methods given for detecting them. 

474 W. C. MILLER [j. s. M. P. E. 

Some of the most insidious evils that need not, and should not, be 
tolerated will be so specified. But the degree to which the other cor- 
rections must be carried is, of necessity, left to the user's own good 

The fundamental principle to be kept in mind when using modern 
lenses and panchromatic film stock is that all colors to which the film 
is sensitive must come, within small limits, to a common focus. Mod- 
ern lenses can be held within such small tolerances in this respect 
that there should be no detectable discrepancy between the foci of 
the red, the green, and the blue light when the lens is tested photo- 
graphically on a suitable target. 

A satisfactory target for this test can be made by ruling on a white 
card of adequate size a series of parallel, horizontal lines separated by 
about an inch and numbered each way from the center-line. This 
target is set up a short distance in front of the camera at an inclina- 
tion of about 45 degrees and evenly illuminated. With the lens fo- 
cused on the central line, a series of exposures is made of this target, 
using a standard set of tricolor filters. No change should be made in 
the focal setting of the lens between exposures. Any change of the 
relative sharpness of the lines of the target seen on the resulting nega- 
tives is an indication of the extent by which the various colors fail to 
come to a common focus. There should be no detectable difference 
in any of the three images taken with a good lens. If some color fails 
in actual practice to come to a common focus when the lens is used 
with panchromatic stock, the resulting image will not be sharp and 

For lenses that are to be used only with stock sensitive to the blue 
or blue-green this restriction is not so great, for in that case should the 
red light fail to come to the same focus as the blue and green, the pho- 
tographic image would not suffer as the film is insensitive to the red. 
It is therefore unnecessary to pay the extra price for panchromatic 
lenses unless they are to be used with panchromatic stock. 

When a lens is focused wide open the image may be as sharp and 
clear as desired; but when the iris is stopped down preparatory to 
making the exposure, the images formed by some lenses will be found 
to go out of focus without any movement of the lens itself. This is 
due to zonal spherical aberration in the lens, and is often called "dia- 
phragm focus." To recapture the sharpest possible image it is neces- 
sary to refocus the lens, using the aperture at which the exposure is to 
be made. 


In selecting new lenses a series of exposures should be made of the 
test-chart used in the color test, first with the lens wide open at its 
best visual focus, and then at selected smaller apertures with no 
change in the focal setting of the lens. Upon examination of the 
negatives, the change in the apparent focus of any of the exposures 
should be negligibly small. Most of the modern fast lenses show this 
"diaphragm focus" to a greater or lesser degree. The user must de- 
termine just how much he can tolerate. 

Any lens already in use that displays diaphragm focus should al- 
ways be focused at the aperture at which the exposure is to be made. 
This is often difficult to do when a small stop is required, but it is the 
only way to be sure that diaphragm focus will not influence the sharp- 
ness of the picture. 

Some types of lenses show a tendency toward internal reflections 
that give rise to "flares" or "ghosts." Such a tendency can be de- 
tected easily by placing a ground glass in the focal plane of the lens 
and moving a bright light some distance in front of the lens all about 
the field of view while watching the ground glass. 

Any tendency of a lens to produce flares in actual use will be greatly 
enhanced and the relative merits of various makes can be judged. 
Generally the fewer air-glass surfaces there are, the less is the tendency 
to cause flares. Consequently slow lenses of the three-element type 
should be favored when a scene requiring great contrasts is to be 
photographed . 

All lenses possess a characteristic that finds such frequent use that, 
although it is in nowise a test, it deserves mention here. When a lens 
is focused upon a point A a given distance away, other points lying 
short distances in front of and behind A will also be in fair focus. It 
is found that the focus carries with reasonable sharpness a greater dis- 
tance behind A than in front of it. If two other points, B and C, are 
chosen, one before and one behind A, which are equally sharp, they 
will occupy definitely specified positions with respect to the lens and 
the point A . It is therefore possible to determine just where to focus 
between two objects to make them both appear equally sharp in the 
picture, provided one knows the distances of the two objects from the 
lens. Substituting the distances B and C in the formula 

2B C 

the result is the distance from the lens to the intermediate point A . 

476 W. C. MILLER [j. s. M. P. E. 

As an example assume that one person is standing 10 feet from the 
camera and another 30 feet. A is then 15 feet, and if we focus upon a 
point at that distance, both objects will register with equal sharpness. 
This method gives results that are amply accurate for ordinary use. 
Whether or not the two objects will be perfectly sharp depends, of 
course, upon such factors as the focal length of the lens and the aper- 
ture used. 

The optical definition of a lens, or its ability to render clearly small 
detail within its usable field, is a quality that can vary greatly de- 
pending upon the purpose for which the lens is intended. For por- 
traiture sharp definition is rarely desired, particularly around the 
field. For ordinary work, where that illusive property known as 
"quality" is desired, more definition is needed, but more uniformly 
distributed over the field. For miniatures, process work, or for pic- 
tures that are to be greatly enlarged, every bit of definition that can 
be had is usually required over the entire field. Likewise for optical 
printing and copying. Therefore, depending in what field of work the 
lens is destined to be used, various amounts and distributions of defi- 
nition must be selected. 

To test a lens for definition all that is required is a chart upon which 
are placed cards bearing lines of letters or numbers of gradually de- 
creasing size, much like the Snellen charts used in testing the eyes. 
With these cards distributed advantageously over the chart, exposures 
can be made with the vaiious lenses at their positions of sharpest 
central focus. Care must be taken to see that the test-chart covers 
the entire usable field of the lens in order that the character of the 
image in all parts of the field can be studied. Also the lens must 
shoot squarely at the center of the target, for if it is cocked one way or 
another misleading results will be obtained. 

Examination of the resulting negatives under sufficient magnifica- 
tion will reveal that different types of lenses have different degrees of 
definition in different parts of the field. But it will be found that for 
equal definition at the center some lenses will have much better defi- 
nition at the edges than others. These are said to have better 
"covering power." 

To determine how much definition is required and how it should be 
distributed over the field requires experience and skill. For the un- 
initiated the best way to. determine this quickly is to test lenses that 
are giving satisfactory results in production and to select any new 
lenses that have about the same correction. Experiments with new 


types of lenses may reveal that even better results can be attained with 
some of them. 

A defect often found in lenses is known as "chemical focus." Ex- 
pressed simply, this means that the focal setting determined visually 
does not agree with the one found photographically. In reality it is 
due to peculiarities of the color correction, but it often shows up as if 
it were a separate characteristic. It can be checked by focusing a lens 
visually for best central definition and then making a series of expo- 
sures at the same setting and at others departing by small amounts 
on either side of the visual one. It will be found that steps of 0.001 
inch will be satisfactory. If it is found that the negative having the 
sharpest central definition has a setting other than the visual one the 
lens has the chemical focus of the amount of the discrepancy. In bad 
cases with short-focus lenses this may amount to many thousandths 
of an inch. A lens showing more than two or three thousandths 
should be rejected. 

A lens will be encountered occasionally that vignettes due to im- 
proper construction. Some lenses do so when wide open, the edges of 
the lens mounts cutting in at the corners of the picture. These can 
generally be improved by stopping down the iris. Sometimes vignet- 
ting increases when a lens is stopped down, and is due to the improper 
location of the iris with respect to oblique rays of light passing through 
the lens. 

These two conditions can be checked by making exposures with the 
iris wide open and again stopped down to about //9.O. If the corners 
of either negative are cut in, the lens should be rejected. Obviously, 
care must be taken to insure that no lens shade or matt box in front of 
the lens is the offending member. 

A peculiar effect is obtained with some lenses in motion picture work 
when a scene is "panned." An object entering at one side of the field 
grows or shrinks in size as it moves across the picture, again returning 
to its former size at the other edge. The fault shows itself also when 
the lens is used to photograph architectural subjects : lines near the 
edge of the field are bent either in or out. It is very disconcerting if 
this tendency is pronounced. To obtain good pictures, lenses should 
be used that do not display such a characteristic. A quick way to de- 
termine whether they will or not is to project, by means of the lens 
under test, an accurate aperture plate whose opening is equal to the 
film aperture for which the lens was designed. If the projected image 
of the aperture as seen upon a screen is defined by straight boun- 

478 W. C. MILLER [j. s. M. P. E. 

daries, the lens is free from this trouble. However, if the edges of the 
image are curved, bending either in or out at the middle, this disturb- 
ing effect will be obtained with the lens in use. 

To determine how much distortion is present, measure the height 
of the projected aperture image at one side and again at the center. 
The difference of the measurements divided by the smaller should not 
exceed 0.005. Lenses in which this quantity is as small as 0.001 are 

The effect obtained by panning with lenses having distortion should 
never be confused with the effect of panning about an axis not coinci- 
dent with the optical center of the lens. The latter condition gives 
rise to changes of perspective due to swinging the lens in an arc. This 
also causes certain undesirable effects on the screen. To obtain per- 
fect optical results when panning, the lens must be free from distortion 
and must be swung about a vertical axis running through the optical 
center of the lens. This insures that there will be no disturbing 
changes in the sizes of objects passing across the field and changes in 
perspective and point of view. 

Another test that should be made can best be done in a machinist's 
lathe. The lens should be mounted and accurately centered on the 
threads and shoulder of the lens mount. If a small light is then placed 
in such a position that its reflection can be seen in the various lens 
surfaces, it will often be found that these reflected images will move 
when the lens is rotated slowly in the lathe. When such is the case, 
it indicates that the individual glass elements are not truly centered in 
the cells. Often the effect will be visible in a number of the elements 
at once. 

Although a small eccentricity of the elements is rarely detectable in 
the image, it does have an effect. If several of the elements are eccentric 
the total effect will be very noticeable and undesirable. It takes ex- 
perience to determine how much is tolerable. 

The user or prospective purchaser of the lens should never attempt 
to center the elements in their cells ; it is a job for the manufacturer. 
In fact, lenses should never be taken apart to the extent of removing 
the glass elements from their cells, for they can rarely be put back into 
exactly their original positions. An excellent lens can be spoiled by 
not centering all the elements correctly on the optical axis. 

After years of work with lenses one becomes aware of a quality of 
optical images that can be described only as "contrast" or "bril- 
liance." It is completely separate from the contrast obtained due to 


to the processing of the film or print, and is inherent in the image of 
the lens whether photographed or viewed visually. It makes a great 
difference in the results attainable with a lens whether or not the lens 
possesses this desirable quality. In general, it is due to the type of 
lens : the fewer the number of air-glass surfaces the more brilliant the 
image. But it is due also to other things such as the polish of the lens 
surfaces and their cleanliness, both of which affect the amount of 
diffused and scattered light in the image plane and thereby the bril- 
liance of the image. There is often detectable among lenses of a given 
make and focal length a difference in the contrast of the image. 
In selecting lenses this should be watched for and any lens, however 
perfect otherwise, that gives a flat, dull picture, should be discarded. 

Frequent tests of lenses in constant use will be found very advan- 
tageous. Accidental damage of a minor nature, or looseness of the 
lenses in the mounts due to vibration or shock, can be detected and 
remedied before they become so serious as to impair production. De- 
terioration in optical performance can be detected and traced to its 
source, and can often be remedied if caught in time. The most com- 
mon occurrence of this sort is the "feathering" of the balsam used to 
cement some of the glass elements together. The lenses can be 
cleaned thoroughly when they are tested by someone skilled in this 
type of work. More lenses are damaged by careless or ignorant clean- 
ing than by any other cause. 

Absorbent cotton is cheap, soft, and in every way one of the best 
cleaning materials available. Breathing gently on the surface will 
moisten it and greatly facilitate the removal of dust and spots. 
Cleaning solutions and soaps should be avoided whenever possible. 
Anything that will not yield to the moisture of the breath can be re- 
moved by barely moistening the cotton with carbon tetrachloride. 
Nothing more severe than this should ever be used. Always clean 
lenses with a circular motion, blowing strongly against the surface 
with the last few strokes to remove any lint. 

Careful application of the principles outlined in this paper for the 
selection of lenses will be found to improve greatly the quality of the 
resulting pictures. The results attained on the screen can be no 
better than the lens that made them. It is therefore useless to lavish 
money on sets and costumes that will never show clearly on the screen 
due to poor lenses on the cameras. Greater improvement will be 
obtained in proportion to the required expenditure by using the best 
lenses available and keeping them in good condition by constant care. 


Summary. This report contains the reports of four of the Sub- Committees of the 
Projection Practice Committee, viz., on the Motion Picture Theater Survey, on Screen 
Illumination, on Projection Room Plans, and on the Proposed Revision of the NFPA 
Regulations for Nitrocellulose Motion Picture Film. A preliminary report is ren- 
dered by the Sub-Committees on Theater Survey and Screen Brightness. The Pro- 
jection Room Plans and Revision of the Fire Regulations are presented in full. 

During the past year, the Committee has been engaged in a number 
of important projects, the principal ones being the following: 

(1) Motion picture theater survey. 

(2) Study of screen brightness and methods of measuring it. 
(5) Revision of the Projection Room Plans. 

(4) Revision of NFPA Regulations for Handling Nitrocellulose Motion 
Picture Film. 

(5) Study of the tolerances and clearances permissible in motion picture 
projection equipment and means of measuring and checking these values. 

As these projects involve a great deal of work and require con- 
siderable time for complete study, it will not be possible to report on 
them all at this time. The present report deals only briefly with 
item 1, since, following the publication of the comprehensive theater 
survey last spring, more time is required for analysis of the data and 
formulation of recommendations. With regard to item 2, the Com- 
mittee has long been searching for suitable means of measuring screen 
brightness in theaters, and the present report of the Sub-Committee 
indicates considerable progress in solving the problem. 

Items 3 and 4 are dealt with in great detail in the present report. 
With regard to projection room plans, it is the hope of the Com- 
mittee that all those who contemplate building new projection 
rooms or revamping existing projection rooms, will give serious 
thought to the recommendations contained in these Plans. The 
Fire Regulations are subject to revision pending action by the Com- 
mittee on Hazardous Chemicals and Explosives of the NFPA, to 
whom the proposed revision has been submitted. This matter is 
more fully described in the preamble of the report, on p. 498. 

* Presented at the Fall, 1938, Meeting at Detroit, Mich. ; received September 
20, 1938. 


Work on project 5 has just about begun, so that no more can be 
done at the present time than to state that this subject is receiving 
the earnest attention of one of the Sub-Qommittees. 

The Chairman wishes to commend the various members of the 
Committee who have worked so hard and spent so much time on 
these projects. It is felt that the reports of the Committee presented 
at both this and the last Convention represent contributions of 
major importance to the motion picture industry. 


H. RUBIN, Chairman 


Report of the Sub-Committee on Theater Structures, comprising 
an analysis of a survey of theaters of the industry as regards their 
physical dimensions and structural proportions, was presented at 
the last Convention as was published in the June, 1938, issue of the 
JOURNAL. This report has aroused considerable interest among 
motion picture theater architects both here and abroad. Although 
the work has not yet progressed to the point where the data of the 
survey can be used for determining ideal structural conditions for 
projecting and viewing motion pictures, the work is proceeding and 
it is hoped that the Sub-Committee may be able to report on the 
subject at the next Convention. The subject is a complex one and 
requires very careful analysis. 

In connection with the rising interest throughout the industry 
in good projection and good viewing in motion picture theaters, the 
Projection Practice Committee has thought it advisable to state 
specifically its policy with regard to the view of the screen provided 
for each patron of the theater : 

The Committee regards clear and unobstructed viewing of the 
screen as an essential and major factor in audience satisfaction. It 
disapproves any form of auditorium design or seating arrangement 
that will prevent any patron from seeing all parts of the screen at 
all times, regardless of the positions of other patrons. 

There are several degrees of obstruction of view of the screen. 
Arranged in order of diminishing desirability, these are : 

(1} Clear vision regardless of positions of patrons one or more rows ahead. 
(2) Clear vision regardless of positions of patrons two or more rows ahead. 
(5) Partially obstructed vision under almost any conditions. 


To reduce obstruction of view, there are several methods available, 
including the following : 

(a) Staggering the seats of successive rows (which may reduce the number 
of seats or cause "ragged" aisles). 

(&) Raising the level of each row of seats relative to the row before it (which 
may lead to an impracticable amount of rise in some theaters from front to back). 

(c) Adopting a suitable combination of fall and rise of successive rows of seats 
from front to back (which method requires further study in practice on a wider 
scale under various conditions). 

One or more of these methods should be seriously considered by 
theater architects. In no case does the Projection Practice Com- 
mittee approve any seating arrangement falling appreciably below 
Grade 1 above; that is, the Committee disapproves any noticeable 
obstruction of the screen view of one patron by any other normally 
seated patrons no matter where located. 


B. SCHLANGER, Chairman 


The product that the motion picture theater offers to the public 
is the picture on the screen. The two essential factors in the produc- 
tion of a good screen picture are the film, over which the exhibitor 
has no control, and the projection light. It is only through the pro- 
vision and maintenance of an adequate light-source that the manage- 
ment can exercise control over its product. 

During the past few years theater owners and managers have be- 
come light-conscious. This has brought about the necessity for a 
small, compact, portable, and inexpensive light-meter that can be 
as easily read as the ordinary voltmeter or ammeter. With these 
considerations in mind the Projection Practice Committee set out to 
determine the best type of meter obtainable. 

There are three places at which the light might be measured : 

(1) Directly hi front of the projector. 

(2) Incident upon the picture screen. 

(3) Reflected from the picture screen. 

The provision of a single instrument capable of making all three 
kinds of measurements was considered, and was rejected for the 
reason that such a meter, like all previous instruments, would be too 
cumbersome, complicated, and expensive for general use. On the 
other hand, a meter capable of measuring the light incident upon the 
picture screen fulfills the needs of 95 per cent of the light-measuring 

Nov., 1938] 



requirements. At the same time such a meter is both simple and 
low in price (Fig. 1). 

A meter of this type has been developed, with which is provided a 
visual correction filter which the Committee feels is essential to the 
accurate evaluation of light-sources in terms of human eye response. 
Tests with this meter calibrated in tungsten light at 3000 K showed 
that the errors, when measuring low- and high-intensity arc sources 
were less than 3 per cent.* 

The meter reads from to 30 foot-candles. It was felt that this 
range was ample for present commercial levels of screen illumination 
inasmuch as many theaters do not average 
more than 4 to 8 foot-candles although the 
SMPE recommended average is about 10 to 
20 foot-candles with the shutter running.** 

In using the meter for measuring screen 
illumination, it is recommended that nine 
readings be taken as follows : At the center 
of the screen, at the four corners, and at the 
centers of top, bottom, and both sides. 
When making a measurement the meter is 
held flat against the screen, the cell opening 
facing the projector, with the projector 
shutter running and no film in the gate. 

These readings not only measure the 
incident light but also indicate the uni- 
formity of distribution of the light, which 
is ordinarily expressed as the ratio between 
the readings at a side and at the center. 
A ratio of 80 per cent is considered very good and is obtainable 
by manipulating the optical system of the projector lamp in a 
manner familiar to all projectionists. 


1. Screen illumina- 
tion meter. 


E. R. GEIB, Chairman 

* Of the meters available for such measurements, the one tested by the Sub- 
Committee was the new Weston model 703. 
** Actually 7 to 14 foot-lamberts. 



The projection room plans that follow represent the third revisioi 
of the plans originally published by the Committee in August, 1932 
The second revision appeared in October, 1935. l Such revisions ar< 
necessary from time to time in order to keep pace with the change; 
and developments in the art and practice of projecting sound motior 
pictures. The Committee urgently recommends the adoption o: 
these recommendations by all architects and builders in designing 
and remodeling projection rooms so that greater uniformity of con 
struction and greater efficiency in projection will exist in the future 

In following these recommendations, proper authorities should 
in all cases, be consulted for possible deviation therefrom. An) 
fire-protection requirements specified herein are in accordance witl 
the Regulations of the National Board of Fire Underwriters and th< 
National Electric Code, which should be consulted for details. 

Projection facilities shall consist of (1) the projection room proper 
(2) a film rewind and storage room, (3) a power equipment room 
and (4) a lavatory (Fig. 1). 


(1.1) Construction. The projection room shall be fire-proof, anc 
shall be supported upon or hung from fire-proof structural steel 01 
masonry. It shall have a minimum height of 8 feet and a minimun 
depth of 12 feet. The length of the room shall be governed by th< 
quantity and the kind of equipment to be installed, but shall in n< 
case be less than 16 feet. Consideration should be given to probabli 
future needs. 

The Committee recommends that the projection room prope: 
be so located with respect to the screen that the vertical projectioi 
angle shall not exceed 18 degrees. Optical axes of the projector 
shall be 5 feet apart. When two projectors are used, the optica 
axes shall be equidistant from the center-line of the auditorium 
when three projectors are used, the optical axis of the center projecto: 
shall be on the center-line of the auditorium. 

(1.2) Floor. The floor of the projection room shall be sufficient!] 
strong and solid for the load it is to bear, and shall be constructed ir 
accordance with local building regulations. A generous factor o 
safety should be allowed. A type of construction recommended b} 
the Committee consists of (1) a reinforced concrete floor-slab not lesi 
than 4 inches thick ; (2) a tamped cinder fill above the floor-slab, not lesi 

Nov., 1938] 













V O 








^ / 






IO"x / 
















than 2 inches thick; and (3) a troweled cement finish above the 
cinder fill not less than 2 inches thick. Items (2) and (3) have been 
provided in order to accommodate concealed electrical conduits, which 
should be installed prior to placing the fill and finish. (See Sec. 6.1.) 

(1.3) Walls. The projection room walls shall be built of brick, 
tile, or plaster blocks plastered on the inside with 3 / 4 -inch cement 
plaster, or all concrete. The core of the wall shall be not less than 
4 inches thick. When plaster block is used, it shall be supported 
upon steel framework. All electrical, conduits shall be placed into 
masonry chases in the wall construction so that no pipes shall project 
beyond the main finish line. (See Sec. 6.1.) In all cases, the inside 
surface of the front wall shall be smooth and without structural 
projections. (See Sec. 1.11.) 

(1.4) Doors. A door shall be provided at each end of the pro- 
jection room, at least 2 feet 6 inches wide by 6 feet 8 inches high. 
Doors shall be of the approved 1-hour fire-test type and shall be ar- 
ranged so as to close automatically, swinging outwardly, and shall 
be kept closed at all times when not used for egress or ingress. It 
shall be possible at all times to open either door from the inside 
merely by pushing it. Door jams shall be made of steel. 

(1.5) Windows. Where a projection room is built against the 
exterior wall of a structure, one or more windows may be provided 
in the wall. Window construction shall be entirely of steel, and the 
glass shall be of the shatter-proof type. Metal adjustable louvres or 
other similar means may be used to exclude light. 

(1.6) Ports. (General.) Two ports shall be provided for each 
projector or single-lens stereopticon, one through which the picture 
is projected, known as the "projection port" (see Sec. 1.7), and the 
other for observation of the screen by the projectionist, known as the 
"observation port" (see Sec. 1.8). 

The observation port shall be located above and to the right of the 
projection port. The distance between the horizontal center-lines 
of the projection port and observation port shall be 14 inches; the 
distance between the vertical center-line shall be 21 inches. 

Where separate spotlight or floodlight machines are installed in 
the same projection room with motion picture projectors, not more 
than one port opening (see Sec. 1.9) for each machine shall be pro- 
vided for both the projectionist's view and for the projection of the 
light, but two or more spotlights or floodlights may be operated 
through the same port. 

Nov., 1938] 



(1.7) Projection Ports. The finished ports shall be 10 X 10 
inches, measured on the inside wall (Fig. 1). 

The required height of the center-line of the projection port from 
the floor varies with the make and design of th'e projection and sound 
equipment and also with the projection angle. Manufacturers of 
equipment being considered for the projection room should be con- 
sulted for these dimensions. In no case shall any part of the pro- 
jector be less than 4 inches from the front wall of the projection room. 
Table I lists two constants for various angles of projection which 
when substituted in the formula, will permit calculating the height 
of the center-line of the port from the floor, when certain dimensions 
of the projector are known. 

(1.8) Observation Ports. The finished observation port shall be 
not greater than 12 inches wide X 14 inches high, measured on the 
inside wall of the projection room. 

(1.9) Other Ports. All other ports, such as for effect projectors 


Method of Locating Projector Port 
h = H + rA - DB 














H is the height of the center of the projector pivot from the floor; r is the 
radial distance of the optical center-line above the center of the pivot; D is the 
distance of the center of the pivot from the front wall of the projection room; 
4> is the angle of projection; and h is the required height of the center of the port 
from the floor of the projection room. Select the values of A and B corresponding 
to the angle of projection, and substitute in the formula. 


or spotlamps, shall be as small as practicable, and in no case shall 
exceed 7 1 /* square-feet in area per machine. The location of these 
ports will, of course, be determined by the dimensions of the equip- 
ment and the size and shape of the auditorium and stage, which 
determine the angles through which the light-beams must be pro- 
jected. The dimensions should be obtained from the manufacturers 
of the equipment. 

(1.10) Ceiling. The ceiling shall be constructed of 4-inch con- 
crete slabs or precast concrete, or of 3-inch plaster blocks supported 
by a steel structure and plastered on the inside with 3 /4-inch cement 
plaster. All wiring conduit in the ceiling shall be concealed (see 
Sec. 1.11). 

(1.11) Acoustic Treatment. It is recommended that an approved 
fire-proof acoustic material be used on the walls above a height of 4 
feet from the floor and on the ceiling to reduce the transmission of 
noise into the auditorium. 


(2.1) Construction. The rewind room shall be of fire-proof con- 
struction. It shall have a minimum area of 80 square-feet (Fig. 1). 

(2.2) Floor. See Sec. 1.2. 

(2.3) Walls. See Sec. 1.3. 

(2.4) Doors. The door shall be of the approved 1-hour fire-test 
type, shall be arranged so as to close automatically, swinging out- 
wardly, and shall be kept closed at all times when not used for egress 
or ingress. Door jams shall be made of steel. 

(2.6) Ports. An observation port shall be provided through 
which the motion picture screen may be seen from within the rewind 
room. The port shall be at the same height from the floor as the 
observation ports in the projection room proper, as described in 
Sec. 1.6. 

(2.8) Observation Port. See Sec. 1.8: 

(2.9) Other Ports. An observation window shall be provided 
between the projection room and rewind room, consisting of a fixed, 
fire-proof frame and polished plate wire glass. The window shall 
be not greater than 14 inches square. 

(2.10) Ceiling. See Sec. 1 .10. 

(2.11) Acoustic Treatment See Sec. 1.11. 



(3.1) Construction. The room shall be fire-proof and shall be 
similar in construction to the rewind room (with the exception of the 
openings (see Fig. 1)). The size shall be governed by the quantity 
and kind of equipment to be installed. Consideration should be 
given to probable future needs. 


(4.1) Construction. The lavatory shall be provided with running 
water and modern sanitary facilities, with tiled floor and built-in 
flush-type medicine closet. 


(5.1) General. Two exits shall be provided, one at each end of 
the projection room suite (Fig. 1), permitting direct and unobstructed 
egress, and shall conform to the regulations of local authorities having 
jurisdiction. Any stairs communicating with these exits should 
have risers not in excess of 8 inches and minimum tread of not less 
than 9 l / z inches. The distance between walls should be not less 
than 36 inches. Winding or helical treads should be avoided. A 
platform equal in length to the width of the door shall be provided 
between the door and the first riser. Neither ladders nor scuttles 
or trap-doors should be used as means of entrance or exit. 


(6.1) Locations and Sizes. Locations and sizes of conduits for 
projection, control, and sound equipment are determined by the type 
and design of the equipment. Manufacturers of the equipment 
should be consulted with regard to the proper layout and sizes of the 
conduit systems before floors, walls, and ceilings are finished (see 
Sees. 1.2 and 1.3). Conduits shall in all cases be concealed, and all 
boxes shall be of the flush-mounting type in walls and ceiling. Con- 
duits terminating in the floors should extend 6 inches above the 
finished floor level. 

Conduits and wiring should generally be provided for the following 
circuits : 

( 1 ) Pro j ector mechanism 

(a) motor 

(6) changeover 

(c) pilots 

(2) Projector arcs and spotlights 

(a) rheostats, generators, or rectifier 


(5) Sound equipment 

(a) a-c. power supply 
(&) loud speaker circuits 

(c) amplifier and controls 

(d) ground wire 

(4) Projection room lighting 

(a) general (ceiling and Reelites) 
(6) emergency 

(5) Theater auditorium lighting 

(a) dimmer 
(&) emergency 

(6) Projector ventilation equipment 

(a) normal 

(7) General ventilation system 

(a) normal 
(6) emergency 

(8) Miscellaneous 

(a) stage curtain 

(6) telephone 

(c} buzzer 

(d) receptacles 

Fig. 2 shows the general arrangement of the equipment requiring 
these conduits. 

(6.2) Projection Arc Supply and Location. In cases where the 
projection arc supply consists of rotating machinery generating 
acoustical hum or mechanical vibration, acoustical or mechanical 
insulation will be required. Arc supply equipment should be located 
in the power equipment room adjacent to the projection room, and 
at least four feet from any sound amplifier equipment. 

(6.3) Power Supply to Equipment. Where line-voltage variations 
are greater than 3 per cent, the local power company should be 
requested to rectify the condition. In cases where it is impossible 
to maintain a steady line-voltage into the theater, either manually 
controlled or automatic regulators should be installed. 


(7.1) Projection Room Lighting. Approved vapor-proof ceiling 
fixtures should be installed for general illumination, as indicated in 
Fig. 2, and arranged to be lighted on either the normal or the emer- 
gency lighting circuit. 

An individual vapor-proof relight with wire guard shall be located 
near each projector or spotlamp, as indicated in Fig. 2. 

Nov., 1938] 



All lights in the projection room and associated rooms, shall be 
shaded so as to prevent light from entering the auditorium through 
the ports. 

(7.2) Rewind Room. An approved vapor-proof ceiling fixture 
shall be installed for general illumination. A drop-light or wall 
bracket fixture with approved vapor-proof globe shall be provided 

L'-Si 'qe'HCKAi. 

jg _. JT 

/t.C. COftTKOt- 

F2.OOK. PL /7/V 

FIG. 2. Projection room equipment, showing conduits, ventilation systems, 
lights, and switches. 

(1) Three conduits in floor to a-c. control panel: for pilot light, change- 
over and motor feed, for both projectors. 

(2) Conduit in floor to d-c. control panel and motor generator: for both 
projectors and spot (or stereo) via polarized plug-box on front wall of room. 

(3) Conduit to pipe ground for each projector, and conduit to loud speak- 
ers on stage. 

(4) Vapor-proof ceiling fixtures, and vapor-proof Reelites with wire 
guards for each projector and spot (or stereo). 

(5) Dimmer and emergency lighting control. 

(6) Projector and spot (or stereo) ventilation system and control switch. 

(7) General ventilation system (normal and emergency), with switches 
inside and outside of doors of projection room. 

(8) Wall receptacles. 

(9) Wall switches, two-way type, individually controlling each ceiling light 
fixture from either entrance door. 



near or over the rewind table. These lights should be on a separate 
circuit from the projection room proper. 


(8.1) Arcs or Spotlight. In permanent projection rooms, venti- 
lation shall be provided for the arc lamps independently of the general 
and emergency ventilating system of the room. Each arc lamp 
housing shall be connected by a flue to a common duct, which duct 
shall lead directly out of doors and shall contain an exhaust fan or 
blower having a capacity of at least 50 cubic-feet per minute of air 
for each arc lamp connected thereto. This exhaust fan or blower 
shall be electrically connected to the projection room wiring system 

FIG. 3. Equipment ventilation system: blower capacity 400 cu.-ft. per 
min. ; minimum air movement through lamp houses with blower idle, 15 cu.- 
ft. per min. 

and controlled by a separate switch with pilot lamp within the room. 
There shall at no time be less than 15 cubic-feet of air per minute 
flowing through each lamp house into an exhaust system connected 
to the air outside the building. Fig. 3 shows the general arrange- 
ment of the system. 

(8.2) Projection Room and Rewind Room. General ventilation 
of the projection room and rewind room shall be provided by a duct 
having outlets at one or more points in the ceiling and leading directly 
to the outer air. Said duct shall be capable of maintaining a natural 
circulation of air, without blower or fan, at the rate of not less than 
20 cubic-feet per minute. Auxiliary circulation in said duct shall be 
provided by an exhaust fan or blower having a capacity of not less 
than 200 cubic-feet per minute for normal circulation and having a 
rated capacity of not less than 2000 cubic-feet per minute for operation 
in emergency, i. e., fire. In no case shall the exhaust duct system of 


the room be connected with the ventilating system of the building 
proper. The emergency operation of said fan shall be controlled by 
a switch (Fig. 6) operated automatically by the shutter control 
mechanism when the latter is actuated either manually or by melting 
of the fusible links. This exhaust fan, providing general and emer- 
gency ventilation of the projection room and rewind room shall be 
connected to the emergency lighting circuit of the room, and shall be 
controlled for normal circulation by a switch and pilot lamp within 
the room. 

The ducts shall be of incombustible material, and shall be kept at 
least 2 inches from combustible material or separated therefrom by 
approved non-combustible heat-insulating material, not less than 1 
inch thick. 

FIG. 4. General and emergency ventilation system : normal blower ca- 
pacity 200 cu.-ft. per min.; emergency capacity 2000 cu.-ft. per min. 

(A) Switch and pilot lamp for normal operation, inside projection room ; 
(B) switch and pilot lamp for emetgency operation, outside door of projec- 
tion room; also connected to port fire-shutter control mechanism. 
(Two or more fresh-air intakes required at or near the floor at opposite ends 

of the room) 

Projection rooms and rewind rooms shall have two or more separate 
fresh air intake ducts at or near the floor and at opposite ends of the 
room, entirely independent of and in no way connected to the exhaust 
ducts of the room. Such air intake ducts may be connected into the 
main ventilating system of the building. (See Fig. 4 for general 


(9.1) Construction. Each port opening shall be provided with 
a gravity shutter of approved construction. Said shutter and 
guides shall be made of not less than 10-gauge iron, and the shutter 
should set into the guides not less than 1 inch at sides and bottom 
and overlap the top of the port opening by not less than 1 inch, when 



FIG. 5. Example of port shutter construction. Although this construc- 
tion shows rivets, spot welding is preferable. 

Nov., 1938] 



closed. Guide parts should preferably be welded (see Fig. 5). 
Shutters shall be suspended, arranged, and inter-connected, so that 
all port shutters will close upon the operating of some suitable 
fusible or mechanical releasing device, designed to operate auto- 
matically in case of fire or other contingency requiring immediate 
and complete isolation of the contents of the projection room from 
other portions of the building. Each shutter shall have its own 
individual fusible link directly above it. A fusible link shall be 
located also above each upper projector magazine, which upon operat- 
ing shall close all the shutters. There shall also be provided suitable 
means for manually closing all shutters simultaneously from any 

FIG. 6. One of many possible arrangements of the port fire-shutter con- 
trol. The automatic switch operates the exhaust fan and emergency lights 

projector head and from a point near each door within the projection 
room. Shutters shall be free-acting. Shutters on openings not in 
use shall always be kept closed. Fig. 6 indicates one of many ways 
of arranging the shutter control system. All large shutters such 
as for spotlamps and special-effect machines (when used) shall be 
provided with weights to facilitate operating them manually. 

(9.2) Noise Transmission. The Committee recommends the use 
of means other than glass in projection ports to prevent transmission 
of noise from the projector room to the auditorium, such as reducing 
the free aperture of the port to the minimum size necessary for pro- 
jection by use of fire-proof sound baffles. 

Observation ports shall be fitted with a good grade of plate glass 
set in a metal frame at an angle to the vertical to avoid direct re- 



flection, and easily removable from the inside of the projection room 
for cleaning. The purpose of this glass is to prevent transmission of 
noise into the auditorium. 


(10.1) General. Proper provision shall be made for heating the 
projection room. The same facilities used for heating the theater 
should be extended to the projection room. 

FIG. 7. Rewind room layout, showing required equip- 


(11 .1} Painting. The color of the walls shall be olive green to 
the height of the acoustic plaster. The latter should be painted in 
accordance with the instructions of the manufacturer of the material, 
preferably a dull buff color. The ceiling should likewise be painted 
white. All iron work of the projection ports shall be covered with 
at least two coats of flat black paint. 


(11.2) Floor Covering. Where local regulations permit, the 
floors of the projection room and rewind room should be covered 
with a good grade of battleship linoleum cemented to the floor. The 
floor covering should be laid before the equipment is installed. 


(12.1) Projection Room. All equipment to be used in the pro- 
jection room should be of approved type, including the projectors, 
arc lamps, sound equipment, etc. 

All shelves, furniture, and fixtures within the projection suite shall 
be constructed of metal or other incombustible material. A metal 
container for hot carbon stubs shall be provided. 

Adequate locker space shall also be provided. 

(12.2) Rewind Room. In the rewind room shall be provided an 
approved fire-proof film safe or cabinet, a table, approved rewind 
equipment, a splicer, and approved scrap film can (Fig. 7). 

The film safe or cabinet shall be capable of holding 25,000 feet of 
35-mm. film. 

All tables and racks and all furniture shall be of metal or other non- 
combustible material and should be kept at least 4 inches away from 
any radiator or heating apparatus. Tables shall not be provided 
with racks or shelves beneath them whereon may be kept film or other 

The scrap film can shall have an automatic-closing hinged cover 
and so arranged that the scrap film is kept under water at all times. 

Quantities of collodion, amyl acetate, or other similar inflammable 
cements or liquids kept in the rewind room for the purpose of splicing 
film, shall not exceed x /2 pint. 

No stock of inflammable materials of any sort whatsoever shall 
be permitted within the rewind suite except as specifically mentioned 

All splices of film shall be made with approved mechanical cutting 
and splicing machines. No hand cutting or splicing shall be per- 

Film shall be kept in the film cabinets at all times except when 
being projected or rewound. Any films in addition to those used for 
the current showing or in excess of that permitted by local authorities 
shall be kept in their original shipping containers. 

(12.3) Fire Extinguishing Equipment. Local authorities having 


jurisdiction with regard to fire extinguishing equipment should be 
consulted regarding the proper types, numbers, and locations. 


(13.1) "No smoking" signs should be posted in prominent places 
and matches should not be carried by any employee. 

(13.2) Operation. Motion picture projectors shall be operated 
by and shall be in charge of qualified projectionists who shall not 
be minors. The projectionist should be stationed constantly at the 
operating side of the projector while it is in operation. A proper 
factor of safety in operation, as well as avoidance of imperfect opera- 
tion of projection equipment, or unjustified interruptions of service 
can be attained only by having an adequate personnel in the pro- 
jection room. 

(13.3) Action in Case of Fire. In the event of film fire in the 
projector or elsewhere in a projection or rewind room, the projection- 
ist shall immediately shut down the projector and arc lamps, operate 
the port shutter release at the point nearest him, turn on the audi- 
torium lights, leave the projection room immediately, and notify 
the manager of the theater or building. An automatic switch is 
recommended for the electrical operations mentioned. 


S. HARRIS, Chairman 








For a long time it has been recognized that numerous conflicts 
existed between the provisions of the Regulations of the National Board 
of Fire Underwriters for Nitrocellulose Motion Picture Film and the 
National Electric Code. In addition, when the revision of the Pro- 
jection Room Plans issued by the Projection Practice Committee in 
1935 1 was brought to the attention of the National Fire Protection 
Association, a number of conflicts between the Plans and the Regula- 

* Readers of the JOURNAL are requested to transmit their comments concern- 
ing these revisions to the General Office of the Society. 


tions were discovered. In view of this confusion, steps were taken 
by the NFPA to make their Committee on Hazardous Chemicals and 
Explosives, authors of the Regulations, responsible for the prepara- 
tion of all material relating to motion picture ^fire prevention. All 
such material to appear in future issues of the National Electric 
Code will be taken from the revised Regulations. 

To assist in this work, the Projection Practice Committee of the 
SMPE agreed to submit its recommendations for revising the portions 
of the Regulations pertaining to projection rooms, with respect to 
which most of the conflicts have occurred. 

Such recommendations have been prepared and have been sub- 
mitted to the NFPA Committee on Hazardous Chemicals and Explo- 
sives, of which Mr. A. H. Nuckolls is Chairman. A special sub- 
committee has been appointed by the Committee on Hazardous 
Chemicals and Explosives for considering these recommendations. 
The Chairman of this sub-committee is Mr. George W. Booth, Chief 
Engineer of the National Board of Fire Underwriters, and the per- 
sonnel of the sub -committee includes engineers long experienced in 
the field of fire prevention. The Chairman of the Sub-Committee on 
Projection Room Fire Regulations represents the Projection Practice 
Committee on the NFPA sub-committee. 

The proposed revisions are published herewith for the purpose of 
soliciting expressions of opinion concerning them from the motion 
picture industry. 

In the following proposals, sections of the Regulations pertaining to 
exchanges, studios, storage vaults, etc., not dealing with projection or 
projection rooms, were not considered. Where no change is proposed, 
the section is marked "Unchanged"; added words or clauses are un- 
derlined; sections completely rewritten are marked "Rewritten" ; pro- 
posed new sections are marked "New"; sections recommended for 
deletion are marked "Deleted." 

Attention should be called to one very important departure in these 
proposals : In the original Regulations, structural details of permanent 
projection rooms and temporary projection booths were grouped to- 
gether in the same sections and sub-sections (Sec. 191). The Pro- 
jection Practice Committee deemed it advisable to remove from 
Section 191 all references to temporary projection booths; and since 
it is recommended that the existing Section 192 be deleted from the 
Regulations, the material pertaining to temporary projection booths 
may be assigned to this Section 192. 




Section 11 Construction and Arrangement of Buildings 

(111) (Unchanged) Motion picture film should preferably be stored 
or handled only in buildings of fire-proof construction. 

(114) Exits. It is essential that all rooms in which film is handled 
be provided with adequate aisle space, not less than 30 inches clear, 
wherever walking is necessary between any two pieces of equipment, so as 
to provide safe means of egress. Rooms in which film is handled and 
in which more than two persons work shall have two or more exits, 
remote from each other. Every exit shall be marked Exit in letters 
not less than 6 inches high, or by an illuminated sign with letters of 
the same height 

(115) Vents. All new buildings erected to be used as, and all exist- 
ing buildings remodeled for, film occupancies, except as related to pro- 
jection rooms, rewind rooms, and rooms associated therewith, shall be 
provided in every room, where film is to be stored or handled, with 
vents that will open automatically in case of fire. These should be 
of ample size; they may be in the form of automatic skylights or 
automatic-opening window sash. All rooms, except as aforemen- 
tioned, in which film is stored or handled in existing buildings, shall be 
provided with such vents wherever practicable. 

(117) (Unchanged) Tables and Racks. Tables and racks used in 
connection with the handling of film (joining, inspection, and assem- 
bling tables, for example) shall be of metal or other non-combustible j 
material. They should be kept at least 4 inches away from any radia- 
tors or heating apparatus. Tables shall not be provided with racks 
or shelves underneath them that might be used for keeping film or 
other materials. 

Section 12 Electrical Equipment 

(121) (Unchanged) Artificial illumination in any room where film 
is handled or stored shall be restricted to incandescent electric lights, 
except that arc lights or other forms of electric lights may be used in 

(122) (Unchanged) All electrical wiring and equipment shall con- 
form to the National Electrical Code. Wiring shall be in metal conduit, 
and fuses shall be enclosed. 


(123) ( Unchanged) Lighting fixtures shall be firmly fixed in place, 
and lights shall be protected by vapor-proof globes. All lights shall 
be equipped with keyless sockets and operated by wall switches. 

(125) (Rewritten) Portable electric lamps on extension cords are 
prohibited in any room in wjiich film is handled or stored, except that 
portable electric lamps provided with approved keyless sockets and 
metal protective lamp guards and having service cords of types S 
or SJ with twist-lock plugs are permissible in projection rooms. 

(126) (Unchanged) Motors shall be of the non-sparking type, or 
shall be of an enclosed type, so arranged as to minimize the danger of 

(127) Motion picture projectors and associated electrical equip- 
ment shall be of approved type and safeguarded in accordance with 
the requirements of the National Electric Code, Article 540. 

(128) (New Section) Motor-generator sets, transformers, recti- 
fiers, rheostats, and similar equipment, for the supply or control of 
current to arc lamps on motion picture projectors, shall if practicable 
be located in a room separate from the projection room or booth. 
Such separate room shall be suitably ventilated. No rheostats ex- 
ceeding 30-ampere capacity shall be installed in a projection room or 

Motor-generator sets shall have the commutator end or ends pro- 
tected as provided in the National Electric Code, Section 5310. Rheo- 
stats shall be constructed and installed as provided by the National 
Electric Code, Article 470. 

When motor-generators, transformers, rectifiers, and similar equip- 
ment are installed in the projection room or booth they shall be so 
located and guarded that arcs or sparks caused thereby can not come 
into contact with film, and shall be so located as to provide at least 
30 inches of clear aisle space between any two pieces of equipment 
where walking is necessary. Rheostats for arc lamps (not exceeding 
30-ampere capacity) when installed in the projection room or booth 
shall be installed near the ceiling upon suitably supported heavy 
metal shelves provided with metal pans having upturned sides. The 
rheostats shall be electrically and heat insulated therefrom. 

Section 13 Heating Equipment 

(131) (Unchanged) Artificial heating in any building or room, 
rther than a vault,